Well I didn't get to play either version. My brother has a 3DS but truth be told I wanted to fully appreciate the game in it's entirety on-screen...But I don't have an Xbox 360 or PS3 (not complaining though, I love the Wii still, this is the only game I wanted that wasn't put on it ) But I don't think any more would be added considering the game has been out for ages already
I have only a vague idea of what stages are in there, so forgive me if I list some that are in already. But given the chance I'd like to play modernized HD versions of: Hill Top Zone, Sky Chase Zone, Ice Cap Zone, Carnival Night Zone, Windy Valley (especially for that tornado bit), Red Mountain, Pumpkin Hill (though it would have to be altered to be a Sonic level since originally it was a Knuckles level) Seaside Hill (I thought that was in there, but someone told me it wasn't?) Rail Canyon, Apotos and Eggmanland, just to name a few
I'm honestly kind of surprised there weren't any additional zones made available for DLC for this game. I would have been great to play through Labyrinth, a proper Casino Night (not the pinball table), and either version of Ice Cap.
Some sort of acknowledgement of the handheld games would have been appreciated too, be it a quick run through Sky Base (Sonic 1), Scrambled Egg (Sonic 2), or Sky Canyon (Advance 2).