A lot of the reason champions get updates for visuals is because the older champions fall so far behind that they 'don't fit in'. Pizza feet, for example. I'd say at this point that the fact that lots of champions have less than 40 words of VO full stop, is at that point, and that there should be a team to add a few lines to all these old champs. A dedicated team that at least works towards the 'goal' of expanding the VO would be lovely.
GreenLore8 votesAlternatively I would be happy if they had an animation-update team that added new animations to champs who have already have a model thats up to date,but lacks animations(like shen,singed,alistar who all received a VUs,but didn't receive too many animations)
Beyond Legends1 votesWhat Shen recieved an entirely new model and the rest got only a texture update.
Though Shen and Fiora needs new lines though
GreenLore4 votesUhm no Singed and Alistar also got a completely new model Look at them next to their previous models and you'll see that even though they kept the general design,they still got entirely new models. http://3.bp.blogspot.com/-sUMtuLFvaQE/VLNdQ7KX-EI/AAAAAAAAhEE/Hh2SYLgbz44/s1600/base%2Bali%2Bcompare%2B2.jpg http://2.bp.blogspot.com/-9pchC2HEELc/VDdLd8-ODNI/AAAAAAAAaxQ/EUjGn9wSJ7M/s1600/2.jpg
Sharjo3 votesI'd like this in addition to the OP's point; a VU team that goes back to previously updated champions and brings up the lacking features to modern levels, such as with champions like Maokai, Kassadin, Singed and Shen, giving them completely new animations for everything, new VO and new lore where applicable. Basically updates for folks like Fiora, Sona and Kassadin who got reworked, but more so in kit than in visuals even though they had major visual touch ups.
I know the resources aren't really there for the rework department, but I'd still love to see it someday. Fingers crossed Riot can bring such a team together in the nearish future!
Tesla Effect4 votes
Miss Fortune is such an interesting deep character in lore....the quotes in-game dont really reflect that at all.
Despite his faction not being fully updated yet (Ionia to be specific), Shens story is, and there is a lot of potential for new quotes for this dude, mainly due to all the champions he could interact with (not to mention some neutral monsters).
Have potential for new interesting quotes, mostly for interactions sake.
I expect its a bit harder to give these champs new quotes, mainly due to their factions or even their lore not being updated as well.
Succesfully updated voice overs (various degrees): 
(all pretty much during the larger lore updates)
Zero Skill Tank2 votesAgreed. Some all champions have such few lines that it's sad...
That being said, when Riot VU's the champion, they usually change their lore and general concept a little as well, so they might not be willing to invest time in recording VO that might become obsolete in the future.
Phoenixcresset2 votesOk
Unstoppable Monk1 votesYeah, but how are you going to get the rito buck$ to replace the VO? NA voice actor land definitely costs rent.
XIII Vanitas1 votesSo, are you saying that Riot should pay writers and voice actors just to add few lines of dialogue to champions that could be updated in the future?
Sorry, but I don't agree with you. I'd rather have them spend those resources on another team that does full VGU.
GreenLore3 votesThey could pay writers for champs where they have already a steady direction.
Take Shen for example,the guy got a VGU already and got a lore update,yet his VO has only about 20 lines(if you count his different laughs...)
XIII Vanitas1 votesShen's VO is acceptable, considering the fact that he's not a talkative person.
Are there any other updated champions that could get a new VO?
GreenLore2 votesEven if Shen isn't the most talkactive,it would make sense to add more lines for the sake of diversity(and especially some lines towards Zed,Jhin,Akali and Kennen),because it won't make shen appear stoic if he just repeats the same stuff over and over again. Not to mention that his spirit sword or his ability/duty to fight spirits isn't adressed in the VO at all.
Miss fortune did receive a new lore,a VU and a gameplay update already,but no new VO
In fact a lot of champs received already a new lore,pretty much paving the way for a new VO like 
,etc.
Sure these aren't the worst VOs,but they are pretty outdated by todays standard(heck you know a VO is outdated,when 
s VO is more than thrice as big)
There are also some champs who received already visual updates without added VO or lore like and ,but they could work on their lores together with the voice over(judging by Yoricks taunt for singed they already seem to have a direction for him)
Melledoneus3 votesShen may not be talkative, but his lines are really, REALLY generic.
"There is no dispute." Um. Sure?
"Enforced equilibrium." I suppose, but this one lacks substance.
"Target marked." Missiles engaging.
Seriously, Shen could use some new lines. Especially a taunt towards Zed.
