Would be interesting to see if there does end up being a link. I mean GTA IV was originally supposed to be released in 2007, with work beginning right after SA released in October 2004, and I'm expecting to see GTA V in 2012. I'd be surprised if they had already started planning GTA V so far in advance. The time gap between III, VC and SA was much shorter so they could easily have had a basic plan down for that series.
Would be kinda shit if it was set in France. There's nothing there except wine, bread, windfarms, striped jumpers and silly hats.
I think though, if we get any subtle hints, we'll find them in L.A. Noire.