More detailed stuff here.
Cosmopolitan species, or species that appeared in an iteration of every dex since their creation:
1.Zubat-Golbat-Crobat: My hope is that this guys won't be used for the final villain again. I would much prefer the villain to have no good sides, or if he/she has a good side he/she displays it with his/her teammates, not with another Crobat.
2.Psyduck/Golduck: I hope this guys will be the next cosmopolitan species to a get a Mega, so Golduck can finally get the Psychic type it deserved since Gen I. Outside of that, I don't have much to say expect I hope it gets some more offensive options.
3.Magnemite/Magneton/Magnezone: I feel this line has fulfilled its most capabilities, so I don't expect much from it. I hope it appears alongside more trainers, though.
Its Mega can appear in DP remakes rather in Sun/Moon.
4.Azurill-Marill-Azumarill: I hope these guys are available early on. And I hope they get more Fairy moves, as well as access to Ice Ball from Level-Up.
Azurill can also get Nasty Plot for NU Sap Sipper shenanigans.
5.Heracross: Definitely needs more moves for Skill Link. Getting X-Scissor for in-game would also be very good.
6.Wingull-Pelipper: Same as Magnemite. I can see this line getting a lot more moves, but I don't think most of those will be useful in-game.
7.Nosepass-Probopass: Another species I feel has reached its zenith, the only obvious addition I can see it getting is Head Smash. But I hope it appears with more trainers.
8.Budew-Roselia-Roserade: Sludge with Level Up. That is all.
9.Swablu-Altaria: Brave Bird. That is all.
10. Absol: Its Level-Up scheme needs to be revamped for the confusing levels, but that's about it.
11.Combee-Vespiquen: I doubt they'll appear this time around, but if they do, give Vespiquen a Work Up clone and Psychic. Combee can also get Air Slash and Hurricane, and you know, a male evolution.
12.Buizel-Floatzel: I actually expect this guys to turn up, due to their beach association. Also would be good with Nasty Plot or Work Up.
13.Drifloon-Drifblim: These guys would like a Fire-type move, as well as a Special Flying move.
14.Riolu-Lucario: While they'll likely be here, I have nothing to do with them. Lucario can get a proper Steel move like Meteor Mash or Iron Head though.
15.Skorupi-Drapion: They need some sort of recover move, but that's about it.
16.Croagunk-Toxicroak: They need more Level-Up Fighting moves.
17.Carnivine: Needs to go Roselia route, honestly. It just sucks otherwise.
Other common species:
Four dex species:
1.Abra-line: Assuming they appear, there isn't much to do with them.
2.Goldeen-line: The line can probably get Water Gun, I guess. And Muddy Water, that would be cool.
3.Magikarp-line: Bounce as a Level-Up move. Do it.
4.Geodude-line: Is Okay. Needs more.
5.Tentacool-Tentacruel: Also okay.
6.Machop-line: Gained major boosts in ORAS, so I have no complaints.
7. Grimer-Muk: There isn't much to do with it, honestly.
8. Koffing-Weezing: Same as above.
9. Sandshrew-Sandslash: There isn't much more to do with it, honestly.
10.Igglybuff-line: Igglybuff can get more moves, and the line in all can get more Fairy moves, like Fairy Wind and Moonblast.
11.Staryu-line: Starmie can get moves. Staryu is fine.
12.Vulpix-line: Vulpix can get more Psychic and Fairy moves. Ninetales should get Level-Up moves.
13. Pichu-line: Pichu and Raichu need moves. Pikachu is fine.
14.Pinsir: Pinsir needs Roost. And Megahorn.
15.Rhyhorn-Rhydon-Rhyperior: Rhyhorn is pretty cool right now. There really isn't anything to improve it by moves.
16.Onix-Steelix: It is unlikely that they'll ever give this thing a good Attack boosting move, Recovery move or an easy evolution, so I guess it is complete for now. Only thing we can expect is a boost to Iron Tail.
17.Cleffa-line: Give it Play Rough.
18.Lickitung-Lickilicky: Line needs more early Normal-type attacking moves, like Tackle or Pound.
19. Eevee: Is fairly cool. Each end point has their own issues, which can't be discussed here.
20.Tangela: I hope it is available early on. That's all.
21. Elekid: Same as above.
22. Magby: Same as above.