Thoughts (Please note I'm referring to non-mega formes of the Pokemon I'm discussing):
Altaria sounds pretty meh in PU. Maybe defensive sets work but I doubt it.
Charizard's not going to be in UU for long lol. It was NU last gen and nothing really changed this gen to where it matters. (In fact it got worse in RU due to Houndoom and Delphox outclassing it; Also in NU, there is no Mandibuzz or Alomomola but I don't know if that will Zard broken; Unlike Typhlosion its shit on by Stealth Rock, but otherwise its pretty much the same)
Diancie wasn't very good last time it was in UU. Though due to new toy syndrome its likely not going to be in RU until people start reasoning themselves.
Gardevoir............I seriously don't know this one since its been a long ass time since this was in UU. It was B-rank back then, but it may have new niches in revenge killing Mega Beedrill.
Lopunny.........Support sets maybe but offensively just use Stoutland or Bouffalant LOL.
Manectric's going to be in RU at least. Its coverage in the form of Overheat or Flamethrower give it a niche over Jolteon.
Medicham's good in RU. Nothing's going to change if it move backs down.
Metagross IIRC wasn't very good in UU back when it was in the tier. AV might be decent but I don't know really.
Pinsir was alright in NU I guess. Stuff like Xatu aren't used much anymore so it might be worse the 2nd time around.
Sableye's good in UU. Moving on......
I don't know about Venu IMO since the last time it was UU was in DPP and that was a drastically different metagame than the current UU.
Absol. Will it have enough use over Sneasel? We shall see..........
Aerodactyl sounds cool. Particularly the Stealth Rock sets.
Aggron also sounds cool. Rock Head sets are basically a shittier Tyrantrum but if that leaves it'll be close as a replacement. (Though whether it'll have enough use over Rhyperior I won't know)
Ampharos is going to be in PU. It was mediocre last gen in NU and nothing's really changed in Ampharos' favor.
Beedrill was ass in PU and it still will be.
Blastoise is a shittier Slowking with Rapid Spin. Okay then.
Sceptile was viable during the last stages of XY NU, but it has Shiftry as a form of competition now and Skuntank shits on Sceptile not running Earthquake. (Earthquake is what gives SD its uses over other physical Grass-types. That and Acrobactics to reliably hit Vileplume. Though if Zard comes back to NU it might have to run EdgeQuake coverage instead of Acro, but at least that gives it an item to use)
Sharpedo's going to be good for sure. Though sadly that means RIP Samurott's viability in RU.
Banette I don't see much use in using. In PU you're better off using Dusknoir or Drifblim if you desperately want a physically based Ghost-type. (Which aren't very good right now)
Camerupt in PU sounds neat but its too damn slow in a meta run by stuff like Floatzel.
Glalie as a Spiker sounds interesting. Not much use aside from that though.
Steelix was good in NU back then and its still going to be good now. Its a pain in the ass to face, at least to me anyways.
Audino in PU........... Well there goes Lickilicky's remaining viability.
Chances are these predictions might be completely wrong but who knows.