There have been large waves of splash art and in-game texture updates for just about every champion by now and some have even gotten new ability icons. However, many champion VOs are extremely out of date with less lines than Poppy's jokes and reference to summoners. A mass VO update seems beneficial although I understand that it is harder to do than artwork updates.
I'd love for them to do 
Her VO was made when she was considered a 'joke character' when league was still young. Also, the bilgewater story with 
and the one with 
has fleshed her character out a lot, it would be AMAZING for her to receive a new VO as her current one is extremely out of date.
There was during the Freljord (Ashe, and Anivia) and Shurima (Renekton, Cassiopeia, Sivir, Nasus, and Xerath) events. It kinda skipped the bilgewater event (kinda, since Gangplanks Captain skin sorta counts in).
I would very much like this. Only problem is that Riot sees this and goes "it's expensive".
Usually it's more so on the table for them when they are working on a Champion update. Since you know, hiring VOs, setting up studio time to record and such takes a bit more scheduling then the Splash Arts and other game art.
The only champ who has gotten a VO update without a VU has been Cass. And that was because of the Shurima event more than anything, and it was the only thing of value that ever came out of her rework.
Riot seems more comfortable VUing a champion twice before just updating their voiceovers. It's an ok idea in theory, but in practice it sucks since there have been plenty of champs who have gotten a small scale VU and no updated VOs. It's especially galling on Alistar and Kassadin because they both reference summoners (which are now non-canon) and old abilities (I tried to silence my mother- oh wait, I don't have a silence anymore.)
Yeah, I think Rammus' VO needs some more sultriness to it.
"Ohhhhh.... Kaaaaay....." <3
