On the subject of the game, I hope that there'll be more than Mario, Luigi, Blue Toad, and Yellow Toad available to play as. The way I see it, you offer alternative characters to players who "win" each stage, to keep the competitive field alive. That's what I'd hope, but it wouldn't be difficult to offer a truly robust cast of characters, all having to be earned aside from the default four. There's several characters that can fit in that size frame. I suppose the tricky part is to only allow characters that could ride a Yoshi, which would mean Yoshi likely couldn't be a stand-alone character.
Anyways, the Japanese version of SMB 2, our "The Lost Levels," does have alternative traction and jumping height for Luigi. Super Mario Advance 2: Super Mario World re-implemented these differences, and Luigi also ran slower than Mario did in this game. We've also seen the difference on Wii games, as well. There might have been a card for Super Mario Advance 4: Super Mario Bros. 3 that allowed you to toggle the Luigi differences on and off, you know, via the e-reader.