Having an opera station in GTA III worked because:
- Liberty City in GTA III had the Italian mob in a prominent role
- Rather grey atmosphere
I think opera fulfills a function similar to what jazz did in GTA IV: amusing music in relation to what you're doing in the game. Jazz works well with tense car chases, whereas opera and rampaging around blowing stuff up and whatnot seemed to have some strange relationship.
I don't see the issue with it in GTA V, I just don't think it'll work quite as well as GTA III where it seemed like an unexpected (for a game to include) yet natural theme for a radio station.