According to a rumour started by the blog VG247
, the backdrop for the next GTA will likely be Vinewood (I assume it will include Vinewood, alongside the rest of Los Santos, Rockstar's representation of Los Angeles, or possibly the state of San Andreas as a whole?).
VG247 also stated Rockstar might announce the new GTA at the upcoming Max Payne 3 reveal.
You can read about it here
, although the last link doesn't make much clear...
Don't get your hopes up too high, though. It's just a rumour and I'm sure we're all too familiar with rumours surrounding GTA.