Future CDs, are you excited?
Seeing what could happen, meh. Depends if Niantic wants to get creative.
Salamence: With Outrage, it'll finally fix its problems, but then you realize, it's still a bit soft compared to Dragonite. It will be a formidable pick however.
Togekiss: While this is already unlikely, it won't be able to preform to the levels of other picks unless weather boosted, and even then I'm not even sure it'll beat (future) Azelf and Psystrike Mewtwo in Cloudy weather VS Machamp! (Nor will it beat the big Dragons vs Palkia)
Porygon-Z: It's kind of out of the question whether it'll be relevant. It needs both moves to change for it to actually compete.
Slaking: Slaking on the other hand, has everything it needs to succeed. With the stat nerf, he will become a generalist on the level of pre buffed MM Metagross, albeit unable to hit anything super effectively, or have any resistsances (With a move that isn't Pound) Or they could just give him a charge move.
Rhyperior: How will Sinnoh stones be found? Would one need to save on before the CD? If Rock Wrecker is as good as Frenzy Plant or Meteor Mash, (and it could get nerfed like Blast Burn) it will outclass Ttar, but Rampardos is still king.
Gardevoir/Gallade: If Focus Punch/Disarming Voice is added into the movepools, lots of things will change. Probably will never happen.
There isn't much for 2019, I guess the starters and all that, but then what?
Answers
If you want to hope for the best, then you better believe that a move rework will happen before many potential mons get their exclusive moves.
It seems that you don't really know Gardevoir's situation very well. Every damaging Fairy Move it learns is already in the game and all of them are charge moves. Fairy Wind is not in the game yet, but Ralts cannot learn it. The only other Fairy Moves it learns are status, which we don't know if Niantic will ever implement. If we were to make a prediction using everything that we know so far, Ralts will probably get something like Future Sight as a CD move.
Salamence: Outrage makes it better on paper but would be incredibly boring. I personally hope they go with its other typing and add Fly to the game.
Togekiss/Porygon-Z/Rhyperior: The fact that all of these require evolution items makes me think they're CD ineligible because Niantic won't want to work around that. Togekiss also has its shiny available and with the exception of Pikachu all CD Pokemon have had their shinies released during their CD.
Slaking: Even with a damaging fast move it won't be game-breaking, at least not moreso than MM Metagross already is. Either way I still get enjoyment out of the more casual CD's similar to Mareep and Chikorita days.
Gardevoir/Gallade: This depends on how they handle Gallade's evolution requirement. If it needs an item I doubt we'd see it for the same reasons above with Togekiss/Rhyperior/Porygon-Z. Since the Ralts line can't learn Fairy Wind in the main series your best hope for a fairy fast move would be a rework of an existing one.
