Why is it sad that Miis will be used? Miis are one of Nintendo's biggest successes in years, and I think Wuhu Island would make a great stage. Should a Mii be a playable character? Maybe! Miis have done so much at this point they'd be pretty easy to invent a move set for. To me Smash Bros. games are a celebration of Nintendo's long and varied history, good and bad, and I'd hardly calls Miis bad.
I think this is an exciting time to brainstorm about possibilities for this game, because Sakurai and his team aren't even to this stage of development yet! In theory we'll be hashing out ideas at the same time as the team actually working on the game.
I can't help but wonder who'll get cut and who'll come back. If the jump from Melee to Brawl is any indication, I could see us losing one of the Fire Emblem characters, Lucario getting switched out for Zoarork, and maybe losing Wolf, similarly to how we lost Dr. Mario.
There really haven't been all that many new franchises since Pikmin. Animal Crossing already has coverage with the Smash Town level. Other than that there's the Mii series games, ExciteTruck/Bots and... I think that's it? I'd say Advance Wars deserves a playable character/level.
Playable Ridley. I don't care if he has to be scaled down a little bit, but I want 'im. Metroid needs more than one character, and Ridley is IT! If Bowser can be playable, Ridley can too.
Who knows if we'll see non-Nintendo guest characters again? It'd be cool, but I can also live without 'em. Snake and Sonic would of course be welcome faces again, but I'd for sure trade Snake for:
-classic Mega Man
-Pac-Man
-Simon Belmont
Don't get me wrong, Snake is super cool, but I feel like his contributions are much more about modern(ish) gaming and cinematic gaming, whereas the dudes listed are very old school, and more in line with Nintendo design philosophies. All three of those dudes would also have KILLER levels.