I still think that the next GTA should have some of the feel of GTA 4, after all, if Rockstar go back to San Andreas style, they're actually going to be accused of copying Saint's Row, which isn't going to look good, and a lot of people did actually enjoy GTA 4, for it's flaws, tho I agree the social element has to go, or be made more enjoyable, and the main protagonist needs to be made more fun, or CJ style customisable.
I'm still holding out for GTA : Great Britain, where you start out a lowly cockney criminal, 'snatch' style,and work your way up, eventually needing to branch out, so you fly to the airport, and can go to either Belfast, Manchester, or Glasgow to continue. 4 very different cities with different feels, just connected by a quick cutscene.
For obvious reasons I make the airports a loading screen only, as it doesn't give Fox half an hour of hyperbole about how we're training terrorists.
I don't think it would be too niche, as I think a lot of Americans find Britain interesting, and you could re-use the same old gag about needing subtitles, only this time it's everyone, not just the Rasta guy.