On one side, trading sounds nice. But on the other, it will open a whole lot of problems. And no, I don't agree with IV rerolling there.
Problems list:
1. Cheaters will be trading good stuff for good stuff, while legit players will miss out.
2. Some people will be selling pokemon for money. This could cause quite some legal trouble.
3. We'll have a bunch of noobs running around with legendaries, unless there's a level restriction like "Cannot trade if pokemon is 10 lvls higher than you."
News is slow, so some speculation
If trading introduced this year, could “bad” legendaries have some value? What if when you traded it the IVs were rerolled ranging from 10/10/10 to 15/15/15? If so, couldn’t I trade a friend my bad one for their bad one? At that juncture, would be a good chance they both get better...again speculation/hypothetical scenario
Answers
1. By saying this you are implying that only cheaters have access to the "good stuff."
2. If people got ripped off, well, that's their problem, I don't care, that's what they get for supporting such a stupid practice.
3. I think you forgot the words "maxed out" somewhere in there. An easy fix for preventing people from acquiring maxed-out mons unfairly (especially in the case of multi-accounters/spoofers/bot accounts) would be to reset all traded Pokemon back to their original level or better yet, arbitrarily cut them back to level 20. That way, everyone would think twice about trading across accounts. I.E., a spoofer that has caught and maxed multiple copies of the same high-IV Dragonites, Ttars, etc. in different accounts, would not enjoy the instant benefit of getting all those extra copies into a single account since they would have to spend the candies and stardust on it all over again, making it an inefficient strategy. Same goes for the reverse situation, where a high-level player with an army of maxed out Pokemon could be denied the chance to distribute his collection among several other accounts for better cheating chances, such as multi-account raiding and gym defense. The level cut-off should be even harsher for legendaries... cutting them back to level 15 would be enough to deter people from shamelessly transferring their perfect Kyogre all over the place. That way, people who missed out on some past legendary could still get the Dex entry if someone wanted to help them out with that.
1. That's what you've understood. Not that only them, but they'll have it easier, which means let's say a legit player wants to trade his 100%IV Groudon for a 100%IV insert rare but huntable mon here. His first offer is from a person who scan-spoofed that 100%. He would have received the same offer from a legit player but likely a month later than then.
2. It's not only about people being ripped off. It's about Niantic removing the trade because of it. They might not want people making money off their stuff that way. Or they could ban sellers and buyers but they'd need evidence.
3. I didn't say maxed out because imagine giving even a lvl 20 legendary (yeah I see you said cut them to 15) to a lvl 5 player. That player would then have an easy takeover on gyms, and then they would get bored since they got the legendary without even fighting at a raid for it. They'll even get free legendaries from friends in exchange for a pidgey. In the originals, you actually had to get badges to control something that was higher level and obtained in a trade.
I would prefer Niantic to actually institute a TRAINING mechanism rather than an IV Rerolling system.
As for Trading, I don't think they're ever going to introduce it into PoGo. There is just too much animosity toward Spoofers and Multi-Account players to ever have the player base accept it - and I think it would be a very, very alluring thing for current players to start multi-accounting it themselves. I've got a pretty good data plan, and PoGo doesn't take up nearly as much data as it used to, so putting it on an old phone, putting a hotspot up and then having that second phone in my knapsack while my primary phone is playing could mean I'm hatching 2x the eggs, could mean that I'm catching 2x the Raid Bosses and catching 2x the great wild spawns. Not to mention I would be getting 2x the CTM's, FTM's, Rare Candies, Revives, Pokeballs, etc.
I think it's just too much of a Pandora's Box given how the game has been designed and implemented.