We know he's scheduled
In my opinion I would include the following (in some order)
That's my opinion, visually. Then most heroes need VO updates, but that can come after visuals.
What I sort of wonder is what comes after that?
I mean the way this happened in the first place, was newer heroes looking better because of advancements, right? Wont it start all over again?
I'd like Riot to stop making new champions and just update old ones. A lot of champions could just use some visual updates.
And some of these champions could use some game play updates that are Xin/Azir to Warwick level
Oh and Tahm Kench needs to get constant VO updates for new things in the game :^)
You said what, so I assume the question extends beyond champions.
Bandle City and the Void.
We know that at least &(as a dual update) 
are or at least were at some point on the VGU-list.(though the list is ever changing)
And I do think that all of them need one.
?
VO and Visual Updates for Blitzcrank and Orianna. Lore update for Soraka and Ziggs. We need these desperately.
Varus lore needs some clarity, as there's a lot of confusion for what he is now. Some are saying he is Darkin, some are saying his bow is the Darkin, and so on.. But in terms of visual update and even maybe gameplay update, I would like to also see a visual update to Varus'es particle effects to give a more blight like feel, if you get what I mean.
Also looking at the list of champions, I agree with all of them, in particular..
I hope the next one is . As an ex-Akali main, I feel she's too linear and her kit has little to no complexity. :C
And yes...... He's kind of a joke right now.
Virtually every yordle has been left in Lore Limbo except for Poppy and Kled, though I think Kennen, Corki, Veigar, and Lulu deserve an update the most, since we have an idea of what Ziggs and Donger are up to and the others by comparison don't have severely outdated lore (and Tris has a short story, so there's that too).
How could you forget
Morgana needs one terribly bad
