While everyone knows about the big names in the rework bin of Riot, Yorick, Taric, Urgot, I thought I'd make a list of the champions that Riot's going to eventually rework at some point even though they currently aren't nearly as in need of one as those three.
Not a surprising one for most people. Aatrox suffers from a lot of issues but his biggest ones are that his kit very much a generic fighter one that doesn't combine together to make a particularly unique playstyle and that he doesn't deliver on the kind of fantasy his lore implies you'd get.
Also probably not surprising. Akali's issues are that she's a very binary champion where if she's good or ahead in a game then she's oppressive because of how simple her kit is and because of how hard it is to get away from her. The only things in her kit that make her really stand apart from others is her passive and her shroud. She mostly just doesn't provide a lot of interesting gameplay.
Fiddlesticks doesn't have anything that makes him seem like someone to be reworked on first glance, his gameplay is unique and he's not troublesome to balance. His problem is mobility creep. He's a very slow champion that's main damage source requires the enemy to stay within range of him to let him drain their health. His kit probably won't need a change like Poppy or Sion's as he's got things to bring to a team and he doesn't have toxic aspects to his kit. His issue is just that he needs to be modernized to be able to keep up with how the game works now.
This one also is probably not surprising. Galio is one of the oldest champions and is in need of a story and gameplay update. While he's certainly strong right now when played by someone that understands when to pick him and how to use him, his kit needs to be tightened up and given more focus. He's got crippling mana costs and his kit needs to be given a more defined focus on what he's supposed to be picked for in a teamcomp aside from being good against heavy magic damage teams because of his passive.
Irelia and Xin I am putting together here as they have similar problems. Like Aatrox, actually even more so than Aatrox, they have kits that are very generic fighter type of kits. Xin actually has potential for interesting gameplay due to his ult and passive, but his challenge passive could be redone to be more interesting for both him and his opponent. Irelia is probably worse because so much of her kit is just a generic ball of stats and Riot has said they wish they could do more with her blades.
Tryn is a case where he's frustrating to deal with when he's good and completely ignorable when he's not. His crit passive for early level cheese and his main strategy of just splitpushing all game and then running away if the enemy team comes to stop him or just killing the one person they send after him, along with his ultimate allowing him to duel almost anyone, make him frustrating to deal with. However, Tryn also typically doesn't provide much for his team in a teamfight which is why he's used for this kind of strategy.
While Swain offers a unique kit and he's not unbalanced, chances are that Riot would like to rework him at some point so that his title of Master Tactician factors more into his kit. As he is currently, his kit doesn't take that much thought to use, it's mostly just a matter of judging if an enemy is close enough for you to get all of your spells off on them.
Volibear also somewhat suffers from generic bruiser problems. His kit is also very binary in what it's capable of as it's designed basically just for, "Run in and hit the enemy a bunch" I don't think it would be too difficult to take the abilities he already has though and work with them to create a kit that's more unique and delivers on the idea of an unstoppable bear that rampages through the enemy lines.
So those are the champions I see as being up for reworks by Riot sooner or later. Keep in mind that just because I say these champs are going to be reworked does not mean that I think they're bad champions or that I think less of someone for playing one of them. I'm just looking at this from how Riot probably sees things. So agree, disagree, or add who else you think is up for a rework in the near future.