How much will the attacker list change in Gen 4?

Predictions

Tier 1: Supreme species with great move pools that land them on the top of almost every matchup.

Machamp: Remains the premier attacker against Dark, Ice, Rock, Steel, and the tanky Normal types, despite having lots of competition in Hariyama and Breloom.
Also becomes a good generalist in Cloudy weather.

Dialga: The only Dragon available that can attack into other Dragons without taking super effective damage from the powerful Dragon Tail and Outrage, as well as top generalist, this is what secures it a top spot. (Also will rule Steel types with a good enough moveset)

Palkia: Will come out very close to Rayquaza, but have about double the TDO, also passing Dialga. It will be a top 3 generalist in neutral weather. With a good Water type charge move, it can be a Top 5 Water attacker (Even if it doesnt get a Water fast move)

Rayquaza: Still the games premier generalist, whether the 3 big Dragons in Gen 4 get it the coveted Dragon moveset or not. It's DPS puts it at top generalist, and it's prowess versus pretty much anything is nothing to scoff about.
Kyogre: Is the premier Water attacker, and Water has a wide coverage of raid bosses it's super effective against. It serves as a good generalist, and in the rain it can even rival the Big Dragons.

Mewtwo: Remains the best Psychic type attacker of all generations, also having great Ghost and Fighting movesets to cover a wide range of targets.

Groudon: It was always solid, being the best Ground type attacker of ALL generations. And this time around, it is gifted of being relevant in the raid scene! With Heatran sporting a glaring double weakness, Groudon will undoubtedly be one of the best options available. It will also be a great, tankier option VS Dialga, as Machamp is quite frail against most of it's movesets. (It also has a great Grass type move in Solar Beam, also making it a viable "Grass" type attacker.

Mamoswine: The best Ice type to date, Mamoswine with Avalanche will be one of the games best attackers. With wide type coverage and great E shaped stats, it can be a top 5 counter for almost every boss that's weak to it, and even serve as a great Ground attacker and generalist. (It even beats Kyogre VS Ground type targets like Donphan!)

Rampardos: With its ridiculously high attack stat, this Pokemon rules any matchup it's super effective in. (Unless if the boss has a double weakness to another type) Rock has quite a wide type coverage, making it the optimal counter for many bosses. It shows up near the top in generalist matchups, and in partly cloudy it far surpasses other Pokemon. (Provided it has a double Rock moveset and not Rock Tomb) Fun fact, with Steel moves, it beats Metagross and Jirachi, both of which have STAB!

Tier 2: Are relevant, but don't have as much dominance as above Pokemon

Heatran: Not just a high DPS fire attacker, but a bulky one too. Knowing that it learns Fire Spin and Overheat, we can assume that it will eclipse Moltres and Entei in specialist matchups! The Fire type also has quite wide type coverage, and Heatran sports double resistances to all those types. It also has a resistance to Psychic and Normal, as well as an immunity to Fairy. (That's the entirety of Blissey and Chansey's movesets!) This makes it one of the top counters in clear weather to the tanky Normal types. (Just watch out for Earthquake on Slaking and Snorlax)

Garchomp: While not boasting as much power, as its legendary counterparts Palkia and Dialga, it is still a great non legendary generalist, eclipsing the likes of Dragonite and Salamence. (Assuming it gets DT/O) It will be even better VS Electric types, sporting a triple resistance and (hopefully) super effective moves! In essence, it's the better Flygon.

Regigigas: (Unnerfed) Suprisingly, even with movepool setbacks, this monster rules Normal type DPS and TDO, as well as topping the TDO Fighting charts. (Farewell Hariyama!) It serves as an optimal generalist, (albeit in only one weather, but it's quite common) and a counter to the fat Normal types. (Neutral to all their movesets) Regigigas will undoubtedly be a staple on both generalist and Fighting type teams alike.

Raikou: Even if Electivire gets the moveset it wants, Raikou is still superior, thanks to its bulk. Electivire won't be producing any Kyogre duos anytime soon, and it still does worse against high damaging bosses.

Rhyperior: While usually it will come out below Rock and Ground type toppers Rampardos and Groudon respectively, it still has higher TDO, and good survivability against raid bosses that hit hard. (It probably won't get Rock Slide and Drill Run) Still a solid 2nd rate attacker, that is easier to obtain as well. (Groudon will be out of the raid scene for a while, Rampardos, we don't know how common its evolution will be yet)

Darkrai: Will best Gengar and Tyranitar in specialist matchups, and be a great generalist. It's only downfall is that players can only obtain one.

Tyranitar: Still excels in both Rock and Dark type matchups, and serves as a great counter to many raid bosses. Easier to get en masse than Rampardos, since it had it's own community day. (Also doesn't require an evolution item)

Tier 3: Viable, but are outclassed.

Dragonite: Even if it's outclassed, it's a good counter to Palkia and Rayquaza. But otherwise, there's not much it can do that other Dragons can't do better.

Salamence: With all the same downsides as Dragonite, it's pulled down even further by Draco Meteor, a truly sad fate for such a great Dragon. (It has a higher attack stat than nerfed Dialga!)

Hariyama: A solid attacker from a Fighting type perspective, and still viable for raiding, having its trademark TDO advantage over Machamp. However, it's only better trait than Machamp, it's TDO is done better by Regigigas, it having almost identical DPS.

Gyarados: A top counter VS Groudon with Solar Beam or Earthquake, and Ground types in general. The only reason it's so far down is that Kyogre does everything better in about 90% of matchups, and the fact that it can serve as a great generalist.

Electivire: With higher DPS than Raikou, it puts itself near the top of Tier 3 attackers. But why is it lower than Raikou? Because Raikou has higher bulk for almost identical DPS. (Damage rounding) This fragility makes Raikou a better pick for gyms too, something that which Electivre can't do as well.

Moltres: Although unfortunately outclassed by Heatran, it does slightly better in neutral matchups, and is still a great counter against Grass, Bug, and Steel types.

Porygon-Z: A top generalist in Partly Cloudy weather, it is still worse than Regigigas, despite it not having a Normal type fast move! It's also really glassy, making it's function quite borderline.

Roserade: If given the right movesets, it'll best both Grass and Poison type DPS. The only reasons it finds itself quite low is that those two types don't have good type coverage, and the fact that Roselia is more glass cannon.

Girantina: A bulky Ghost/Dragon type, it does well in both roles. However, it's attack stat is quite lackluster compared to the Dragons and Gengar, making it's DPS worse. That, and the fact it doesnt learn Shadow Claw makes it performance lag behind.

Tangrowth: If given the right moveset, it has great DPS, about on par with Frenzy Plant Venusaur, albeit it bit lower. But what really sells it is its bulk, making its TDO about 40% higher than Venusaur in most matchups.

Venusaur: Until Sceptile gets Frenzy Plant, Venusaur remains the best Grass type attacker. It beats out Kyogre in the sun, making it quite useful in raids. It's use in gyms is quite small though, as many types resist Grass.

Togekiss: If it gets Fairy Wind, it'll a great, high DPS counter to Fighting, Dragon and Dark types. It's double resistances to Dragon and Fighting make it even better. Even so, Psychic, Fighting and Ice types outclass it in its matchups, having better DPS, which is ultimately more important.

Tier 4: Pokemon with usable niches, but there are many better options at this point.

Zapdos: With Thunder Shock, it's quite good (Its Charge Beam variant doesn't make it on the list anymore) and does well in many matchups. The problem is, Magnezone will have the same DPS and better typing, further pushing Zapdos out of style. (There is a good chance it won't receive Wild Charge, though)

Latios: It still has a use in gym battles, but in raids, not really. That is enough of a niche to keep it on the list, however.

Azelf: Who needs Azelf when you have Mewtwo? Still, it will be the second best Psychic type, and it is easier to raid than attempting to get an EX pass, and it's the nail in the coffin for Alakazam. (Needs C/FS)

Espeon: Remains in Tier 4 because its slightly bulkier and has higher TDO, which helps it in raids like Machamp.

Weavile/Glaceon: Like Machamp and Hariyama but for the ice type, these two find themselves so low because of how easy Mamoswine is to obtain. (100 Candy, no evolution item)

Magnezone: Another powerful Electric type, with a plus of good typing. However, if it doesn't receive Wild Charge, it'll perform worse than Charge Beam Zapdos!

Yanmega: Even though Pinsir is better DPS wise, it's dual typing Flying (Which gives an immunity to Focus Blast pokemon like Alakazam and Mewtwo) and better bulk puts it in Tier 4.

Gengar: With a chance of getting Shadow Claw for a research breakthrough, Gengar is back! While being outclassed by Darkrai, it is still easier to obtain. (Despite the legacy issue)

Leafeon: A tanky Grass type, superior to the Exeggcutors. It may be heavily outclassed, but it does have the merit of being easier to obtain.

A bunch of Pokemon that were taken off the list entirely and why:

Entei: Even Blast Burn Charizard outperformed Entei in terms of DPS most of the time, and it's only saving grace was its bulk. Now that Heatran is on the horizon, Entei has no more use.

The Exeggcutors: With Tangrowth and new Eevelution Leafeon performing better, there is no reason to use them anymore. Their dual typing cannot save them anymore, thanks to the new Dragons and Azelf.

Golem/Legacy Omastar: Now that Rhyperior and Rampardos are here, and will outperform them regardless of moves, they don't belong on the tier list anymore.

Gardevoir: If Togekiss gets a Fairy fast move, it's over regardless. Gardevoir never had awesome stats anyway.

Charizard: Heatran says hi.

Alakazam: With yet another setback that is Azelf, Alakazam can no longer be called a premier Psychuc type attacker.

Metagross: Dialga cannot learn Bullet Punch, and even the worst of the possible movesets it can get, (IT/FC) is still better than Metagross. For Psychic, while not totally outclassed bulk wise, a neutrality to Fighting is what brings it down. (Does have a minuscule niche VS Poison types that don't have Ground sub typing like.... Muk.)

This is my opinion, and you guys can comment on whether you like it or not.