Majora's Mask Link with the ability to turn into Fierce Deity Link
Mewtwo with a move set that doesn't suck
Ghirahim
Demise
Midna
Geno
Ridley
Sonic
and that's all I can think of at the moment.

Uuh... thats tough for me...

I would like to see a SE character... not necesarily from Final Fantasy or Kingdom Hearts... Sprite from Secret of Mana would be fun :D

Some cool ideas here. I'd like young link/toon link to stay, but be the same character with alt costumes. I've always wanted simon belmont and pacman. I also would like snake and sonic to return, but that's all for 3rd parties (this time around. i'd love megaman in 10years).
Link with a final smash turning into fierce deity link, as well as gannondorf turning into demise. I'd love to see ghirahim or Zant. Ooh, or ghirahim incorporated into the ganondorf/demise transformation as his weapon. Tingle, Midna, Groose or the rebels from TP would be cool assist trophies.
I'd like to cut back on the pokemon. jiggly, pikachu and lucario or mewtwo, Or maybe a mew2Lucario tag team/transformation move.
Little mac is a definate with a gigaMac final smash. Last 1st party i can think of is louie from pikmin 2.
I don't think K rool or ridley as characters will work just because they were too big. Then again you could make the argument that Bowser was too big if you go by his 3d mario series representation. But those 2 have been double the size of their respective protagonists in all the games i can think of.
I really don't like the idea of custom characters or original characters just because i think that defeats the very purpose of the game. However, additions i'm practically begging for are special tag team smashes for particular teams, and 4 on 4 online team games. So long as the new wii-u network is up to par i don't see why that would be a problem. I think 4 on 4 games would be so killer

come to think of it i think dillon the armadillo might be suitable as well, although not very well known as far as 3rd parties go, and that seems to be the prerequisite for being a 3rd party smash bros. character.

Sora would be quite cool!
I would like a re-imagined Pokemon Trainer also. All of the existing ones from Brawl + Tom Nook... yes! That would be the best SSB Ever! Tom Nook could use his pedo and money controlling powers against you!

Goku
Naruto
Luffy
Natsu
Ichigo
Sora
Phoenix ace attorney
Ken
Ryu
Mickey mouse
Digimon..

Travis Touchdown
That would be amazing! :O

Goku would be awesome! His final smash could be spirit bomb or Kamehameha!

I think all of those are a little too hopeful. XD

I like your picks!  But, I would add a few: Viewtiful Joe, Grodus or Crump from Paper Mario 2, and Tubba Blubba