Honestly, Generations felt like an extension of the Adventure gameplay style as it was, anyway. I mean, sure, it's just Sonic, no Tails or Knuckles, but Sonic's gameplay didn't really feel too far off (provided you replace the Spin Dash with the boost like Sega's been wont to do lately). I'm not sure that adding wildly different gameplay styles is really in the series' best interest anymore; the last time they did this, Unleashed, it backfired horribly (the Man-Hog isn't horrible, but fairly tedious, and either way was cited as the largest problem with the game in many reviews). Instead, finding ways to make Tails and Knuckles work with the Unleashed/Generations gameplay might be in their best interest - although since neither can boost (or at any rate, neither should boost), they'll really need to step up how tight the controls are when not boosting. From what I played of Generations, the not-boosting controls didn't feel right, but I can't really tell if they're too tight or too loose...