Sonic Adventure and Sonic Adventure 2 are already on Steam. There's your Dreamcast era.
Yeah well that makes no sense. By that logic, no need to mod Mario into Sonic Generations since you can just play a Mario game. But actually playing as Mario in Sonic Generations is apparently exactly like playing Sonic Generations.. so why not just play Sonic Generations.
Also I had to check the trailer again just now to see what the classic level gameplay is like, but would you believe that the trailer is 100% Modern levels?? ARE YOU KIDDING ME. You'd think they'd add Mario to classic stages and that would have actually allowed Mario to play somewhat like Mario.
And hey I'm no purist, there's nothing wrong with reinventing what Mario could/should play like. But they just ripped off the gameplay that's already in Sonic Generations. There's nothing different about it. Like the ones that exist that let us play as Shadow the Hedgehog or Mega Man X, or presumably countless other characters, while playing nothing like how those characters actually would. And that's just talking about Sonic Generations. People have modded Sonic Adventure 1 too, so that Shadow is playable in it. But the mod is lame because he moves like Sonic does, not to mention there are all sorts of things they could have fixed about the game instead of making pointless skin swaps. Same logic applies here.