Sonic Generations HD, Jesus it's crime it never happened...
I'm almost entirely convinced they had an extremely rigid deal involving the music licensing. I guess they're still beholden to Dreams Come True and others.
And yes, here's some ideas for DLC:
1. Music Packs
Because as long as they had the rights cleared, this would be a ridiculously easy way for them to make tons of money. They need to patch Trial Mode so that you can play custom music during it, though. What an odd oversight on their part.
2. Character Skins
Quick and relatively easy. Sonic Generations already has this functionality pretty much built in. Yes, I know, "shitty friends", but they would all just function as Sonic does with some different graphical flourishes. Basically, sell an official version of
this. Maybe restrict them to Trial Mode to get around the "talking with Sonic's voice" cutscenes.
3. More Zones
These were apparently expensive to make, but still, Icecap would be worth it. Especially since they could hit two zones with that, Classic being Sonic 3, Modern being Sonic Adventure. A lot of the ice graphical effects and mechanics are already in the engine, thanks to it being shared from Unleashed. I just hope
Hard Times doesn't make getting the music too much of a pain.
Another idea would be to create an amalgam zone, mixing up elements from different stages into a single zone, implying time was starting to collapse, positioned right before the final boss. The final boss includes chunks of different zones flying by (you probably hardly noticed these because the boss fight is a giant mess), so this would be extending that theme. And it could be called...
...Okay, "Clock
Work Zone". An unused name for an original Sonic 1 level, relating to clocks, in a game about traveling through the series history, I think it works pretty well.
4. More Missions
More along the lines of the "Action Master" mission, which was a good balance of testing platforming ability without being too painful.
5. Port in Unleashed Daytime levels
Because it's already been done. We've seen fans do it 90% of the way, and Sega would have access to the source code and source files, so they'd have a far easier time, and be able to accurately modify the engine and include new elements as they needed. Include the DLC levels too, if possible.
All of this content would also make it easier to resell the game on PS4, Xbox One, and possibly Wii U. DLC on PC would be expected, on PS3 and 360 would be nice.