Next gen wont be backwards compatible, but I'm sure you can buy downloadable games that will run on the PS4/XBOX One system.
GTA V will be out for next gen, someone found the script for it in the xbox 360 game, so it's coming to PS4 at least.
GT6 will end up on PS4 as well, but more than likely be GT7, which they said will take them only a year or two to make, PS4 is very easy to code for, much more like a PC, so expect GT7 within a year or two and GTA V within 6 months on next gen.
Goodbye stupidly long development times for GT! The PS3 was a pain to code for apparently because it was overly complicated.
You could tell though, GT6 IMO looks almost next gen.