I think Ezreal's revamp was the healthiest we've ever seen. It did nothing to change him, it only improved on what he had and expanded his fantasy. I absolutely believe a large amount of champions need exactly that.
So, who would be first in your guys' book?
I say 
only because I'm partial towards her and I'm exhausted of the same 18 voice lines and imaging the endless possibilities for a Noxian elite-tier assassin fantasy.
(she's already getting it)
Top of my list is 
. Reav3's talked about him being on that list and I definitely think he needs it the most, what with his lore personality being completely opposite to how he acts in-game. I'd like to see his visuals reflect the fact that he's a cobbled-together scrap golem from Zaun, too.
Every champion that hasn't gotten a gameplay update since before Season 3
Kassadin is top of that list.
I think 
and maybee 
. Their kits don't need much changes and they could use the facelift and modern VO/Interactions.
I know 
received a VU already but I think her cougar form should feel like an actual champion (and not a pet) . It should have better animations and feel like a predator the way Warwick does.
and 
also received VUs, but I feel they could be more in-line with their modern depcitions in the lore and get some minor kit adjustments.
Volibear
All of these champions unfortunately received half-assed work to them that SHOULD have been Ezreal level VGUs, but instead just slapped new paint on ugly VOs and animations and got updated kits, and then were left in the gutters.
Not. a. single. one. has a recall animation. None of them have homeguards. Maokai's voice was only updated because Swain's voice actor was on site and they realized they could do Maokai as a side gig.
All of these champions need to have their animations broken down and replaced entirely by a while new rigging. I mean, at least Aatrox was newer and most of his movements could be preserved without having him look weird, but even still, a huge chunk of how he moves WAS replaced with his VGU. But when someone like Miss Fortune and Fiora don't have seamless dance animations that don't clip the model horrendously in the process, I consider that a design fail. And Shen still runs with that horrible clipped heel trot, while Singed look like he's having a seizure when he's dancing. And that's not event discussing the like 8 voice lines that Singed and Alistar have, nor Sona and Miss Fortune's continued insistence on calling you Summoner. They're all in a poor state, and Riot for some reason considers this acceptable. They're not modernized. They just look fancy, but the underbelly of the beast is old and rotting. They need to be fixed and completed.
His E needs an active ability, even if it's something small, and his W could use some fine tuning. I'd like the card cycling to be more predictable (always start on the same card and put the Gold card last in the cycle to compensate.)
i wish riot would work on all of them at the same time and release them all at the same time on one big patch
or 
Thinking more into it, if they ever updated both Kat and Talon they could definitely be similar and un-similar in defining ways. Katarina was trained to be an assassin, while Talon honed his skills on the streets of Noxus and was later adopted into an assassins family.
Kats animations would have form and precision, while Talons would be vicious and possibly rely on dirty fighting tactics.
As for weaponry, neither of them actually match Noxian weaponry (as seen in Noxus lore universe page) so they could have similar weapons
My list with some detailed explanation:
Caitlyn's kit is fine, albeit there's some changes I'd PERSONALLY make (but that's my feel). As she is, her kit works fine and she's got a nice niche. However, she could use some love as her model is a Season 1 disasterpiece and as the first true "Piltover" champion, she's what happens when you fill a shotgun with steampunk aesthetics and fire indiscriminately.
Not much to say about this one. Iconic kit. Good champ and there's been plenty of cinematics and appearances of the steam golem that show you can easily give his design a razor-sheen polish to make him look spiffy.
Another workable kit, Ashe was also one of the first Fridgelord champs. Her design might need some more fine tuning like giving her some clothes that better fit her regal title as an "avatar of avarosa" but I wouldn't want to stray too far in the fear of ruining something a lot of people earnestly love about the character. Plus miniskirt. Maybe axe that.
While Jarvan's design is killer and it aged pretty decently, I also think he's got some problems. Namely the black armor/aesthetics that don't really fit Demacia's theme of white/blue/gold that they have. Not a huge change I'd make to ol' J4 but some color correction and maybe some cool stuff to better fit his character like thicker armor.
Untouchable (btw) because of his rabid fanbase, I do think Jax could use some touchups to look less like a walking eggplant and more like a timeless warrior from a lost nation. Hell, you could just take his current design and add some tattered/raggedness to it and he'd be an S-tier design. All Jax really needs is a five dollar coupon to a clothing store.
Noc's kit has aged pretty well and he sees play (which is good!) but his visuals have aged like Milk and the angry inkblot could use some love. He's also in the unique spot where Noc's appearance leads to him being a very open-ended idea of a character. I'd like for Riot to home in on one thing and really make him emphasize that.
The last rework (
) was shit. Give her a new one guys.
I just want his bugs fixed, his hasted movements to match his blood trail, and some changes to his skins that many warwick mains complained about but small communities dont matter to Riot.
rework her ultimate please.
neekos decoy should be wukongs decoy, there I said it.
make his e break free from slows again please. He completely lost his paladin style.
add a passive to his shrooms that every third shroom also creates a bush so Teemo can utilize his passive better.
I want 
to get new models/animations since she only has like 4 useable skins, but top of my list is . She was the first champion VU and could use another one, with her lore update etc., and updates to her kit (maybe just her shield). Plus she has 1820 skin thats worse than a 975 skin.
I have a bookmark of the top priority riot lost.
But if it helps Kat's getting a revamped running animation.
