http://www.gtplanet.net/gran-turismo-6-gameplay-footage-and-hands-on-impressions/
Watching this game play footage, I came to a very narrow minded conclusion (because I don't play racing games, and GT5 I bought for $10 is still sitting there on my shelf) that the PS3 GT6 will be sold as game with a new different feel to it. Some GT5 players may end up like it, some will may not. It will depend on taste.
I guess what I really want to say is that GT6 will be vanilla version of their new game engine. They will test to see how well it is received, improve on it through community support, let GT fans get accustomed to the changes and 2 years later, they will release GT6 on PS4 which will basically have all the eye-candy, community suggestions/improvements & added content.
I don't think they are beta testing with the PS3, I just think they want an opportunity to get as much feedback as possible on their new engine & Ideas, but they don't want to give away their hard work for free. They will use the feedback to try to improve the game as best they can for the PS4.
I think most of those that play GT6 will start parsing the feel of the ride over past GT iterations and that will sell the game on PS3, which will set up a huge install base for the PS4 version and all if its improvements.
