Most of the Champions VGU had gain new Voice Actors. But on Irelia's case, I think this should not be done. Her Voice Actress delivers Irelia with such a strong personality. She is Irelia (specialy when she screams when using Blade Surge and Transcendence Blades). So Riot please, do not change Irelias Voice Actress on the VGU, I'm sure she will do a phenomenal work with the new voice lines! (
My blade is at your service! 
RiotReav315 votesWe will take the same stance we take on all our VGUs on Irelia.
If the same voice actress is available and interested and can legally audition (We don't do Union, for example) we generally let them audition.
We usually have a lot of people audition though and we will end up going with whoever performs the role best and hits the new direction/personality of the VGU. It's hard to tell if a actor or actress has enough range to hit our newer, longer scripts just based on the small amount of VO lines our older champions have. Many times the old VO actors/actresses either can't hit the range of a longer script or they just don't match the new personality/theme of the updated champion.
You Are Cute XD4 votesWhy no union? This sort of stance leads one to question Riot's integrity when trying to unionize the players.
Variks the Loyal7 votesI'm pretty sure it has to do with royalties and other stuff. Most games can afford to give royalties to a VO based on how many copies the game sells and how often the character appears in the game. With LoL, it doesn't work that way, and you can't, for example, pay a royalty each time the champion in question is bought by a player, the cost would add up WAY too high.
VOs also aren't creditted in LoL, for other reasons, but the actors are obviously recognizable and are free to come out and say, "Hey, I voice this champion." Happened with Matthew Mercer and Gangplank, I think.
WiccanBKaplan2 votesMatt is the voice of Wolf I think.
Variks the Loyal2 votesYes he is, Yorick as well.
EROTIC RAID BOSS3 votesWhat do you mean don't do union? You don't take actors who are unionized? Even though you pretty much just need then to do one recording session for their champ and then they're done? That seems bizarre
Thryale3 votesHow does one audition for champ VO? I know I have zero experience in such things, but I always thought it'd be cool to voice a champ, or at least try. XD
Solidair37 votesAre you able to expound on why you don't do Union?
Additionally, Irelia's theme is very cool, but she currently doesn't deliver. Her story is also interesting, so I'm curious if the plan is to overhaul her personality very much?
I feel gameplay and meeting her theme in gameplay is the only place she is lacking.
Raxistaicho1 votesWendee Lee.
RenanRein3 votesThanks for the the answer! Oh I understand. Well, lets hope she is available and can hit the quality you guys are expecting.
Another thing Reav3: I did a topic on Irelia's subreddit about some of her key elements: thematically and Gameplay Wise, I would be very happy and pleased if you take a look, who knows this feedback can help you guys with some insights for her update!
Thanks for your time!