Even if it'd be expensive to get it going across multiple languages, I still think Riot should go for it. It'd be extremely profitable to let people purchase unique announcers, as the standard one has gotten bland by this point.
In particular, I'd love to hear a KLED announcer. You could get so much comedy out of it. I'll have a sample of what I'd have him say in the comments below.
When playing Heroes of the Storm, I love using the custom announcers that are available. The Alarak announcer, in particular, is so damn good.