Here's my thoughts:
1. It would be VERY surprising to NOT hear anything at TSG on the GT series. That's PD's and Sony's home court show. And with Forza Horizon coming out and Forza 4's success, PD/Sony needs to get some of those fans and momentum back. I know I've been enjoying Forza 4 and am quite looking forward to see what Horizon has to offer since I haven't really heard or seen anything worth while from GT as of late.
2. GT6 on PS3 would be a little surprising this late in the PS3 life cycle. But that would reveal a high possibility of PS4 being to some extent backwards compatible. I can't see a slow grind, long development cycle game like GT being released on the current gen right before the release of the next gen.
3. I think there will be a massive GT5 update as the swan-song??? per se for GT5. Possibly multiple new tracks (not different configurations of the same track) with day/night AND weather for them all, more cars (more than just 4 or 5, and not another Mini or GT-R or Miata or FT-86 clone), and possibly new features (multi-class racing for one because that really doesn't seem hard to do). More cars are a definite welcome especially with recent and non-Japanese cars like 2013 Shelby GT500 (Mr. Shelby just passed away so Kaz might honor him by putting this car in ... I hope), Audi RS5, Ferrari F12 Berlinetta, etc. I'm not wish listing (maybe a little), but the cars available definitely need to be updated with the times to take back some of the thunder GT once had. Forza is killing GT is this department. Don't have Porsche? Do what FM4 did with RUF. I just don't understand why ... I'll stop right there. *breath in, breath out, breath in, breath out*
All in all, I think GT5 3.0, or whatever you want to call it, would be the best thing at this point. GT6 can have now and all the rest of the time till PS4 to be worked on. Now if there is a GT Vita, I'm going to be pissed. That means there is no focus on GT6 and GT5. PD is spread thin as is. Besides, GT IMO was never meant for a hand-held. Playing GT without a wheel takes away from the game and immersion. It's fine on console, but GT should always have wheel available.