So, here's my point of view on the whole thing:
At first, I seriously don't expect GT7 to be released this year, I'd say it comes within the first quarter of 2016. Surely, releasing the game at the end 2015 would be quite rewarding in terms of money, if you know what I mean. But I hope they've learned something from GT6 and release it a bit later then everyone is expecting, so the game is already filled with some good features right away. But only a bit, not like GT5 (they said it'll come in 2006, then delayed it again to 2009, then again to 2010 when it finally came out). Then we have the features. Let's take the Course Maker for example. In GT5 it was playable right away, but in GT6 it still hasn't been implemented. I mean, the Course Maker on GT5 was actually not that bad, so why didn't they just took GT5's Course Maker, added some extra features to it (Point-to-Point races, like they were mentioned on a screenshot of GT5's CM but for somewhat reason was not in the final game) and just bring it to GT6. Well, the CM has been in Beta testing since the end of June 2014 and all that stuff, but hey: I don't want to get too much off topic.
Livery Editor. One of the most anticipated features people want to see in Gran Turismo. Kaz announced a Livery Editor to appear in GT5 at TGS 2006. Did it came? No. So I don't really expect it to come in GT7, too. Although it has been said that GT7 will be the best game of the GT franchise yet, it has also been said that players can do things that couldn't been done in previous GT's. So, does it raise my hope for a Livery Editor? Well, kind of. There is a chance, but then there isn't one. We'll see what the E3 brings to us.
Cars. Kaz already said back in 2014 that GT7 will still feature Standards. Some people might don't have a problem with that, but keep in mind: a PS4 game with cars that were modelled more than 10 years ago? But okay, PD even had the decency to bring a Standard as a new car to GT5. So, always expect the unexpected. Anyway, I'm hoping that they'll semi-premiumize most of the Standards and maybe, even update some of them like they did with the Bentley Speed 8 in GT6. There are so many cars that deserve to be a premium car, for example the Supra, the Calsonic R32 just to name a few. Also, PD should get rid of some cars. Almost 150 Nissan's? Come on PD. We don't need 15 different models from one model type. Example: Skyline R34's. There are several R34's in the game. From '99 to '02. We have normal GT-R's, we have M-Spec's, we have V-Spec's. Three or four or just the most important models would be more than enough. I prefer Quality over quantity instead of Quantity quality. In terms of PD adding new cars, I'm expecting (as one user mentioned before) 150-200 new cars to come, from new SuperGT's over some new road racers to some new LMP's and maybe maybe, even some 2014 or even 2015 NASCAR's. For me as a NASCAR fan, it would be pretty amazing to see some Xfinity cars or even some CWTS trucks appear in the game. Which will lead us right to the tracks. GT6 already has a great variety of race tracks from all over the world and beyond (fictional tracks), but the more and more I drive them, I (and maybe some others) get bored of them. You know, the Ring is the most loved/driven track by GT players (I suppose), and probably will ever be it. But I'd really like to see some more NASCAR tracks, for example some short tracks (Martinsville for example) over some 1.5 milers (Atlanta or Charlotte) to Talladega. In terms of Circuits, I'd like to see Sebring or Hockenheim in GT7, there are so many people would like to see appear in the upcoming title. But you can't have it all, sadly. Take Seattle for example, the track literally everyone (me included) wants to have back. It was barely shown in the NSX Concept trailer from GT5, like Apricot Hill was shown in the same trailer and Willow Springs in the Corvette trailer. Willow Springs and Apricot Hill both came in GT6, AH even made it's long awaited comeback to GT. Maybe we'll see some comebacks then.
What players also desperately want: better car sounds. PD delivered some good ones on several cars in GT6, like with the R8 LMS Ultra or the VGT's (the later ones, counting from the Subie from November or October 2014). They have a new sound recording technology called AES, so they better use it for recording car sounds for GT7.
And then there are graphics. I have to say: the graphics on GT6 are defintely awesome. Nice textures, (most of the time) good shadows, and Adaptive Tesselation on some of the cars that came with GT6 (especially the VGT's) takes the graphical level of the cars very high. I'm expecting Adaptive Tesselation and better paint effects for GT7 then.