Alright, how would you feel about this? 52 characters (55 when Miis are usable), on the larger side (at least for me), considers Gematsu Leak, considers other "hints" that could be straw grasping, 4 cuts (Lucas, Snake, Squirtle, Ivysaur), and Jigglypuff retiring (only to be brought out of retirement as first DLC character). Miis and random share a slot.
Blue - confirmed returning vet.
Red - unconfirmed vet.
Green - confirmed newcomer.
Yellow - unconfirmed newcomer.
Purple - unconfirmed, have made an appearance/ related to Gematsu Leak.
I particularly think the arrangement fits nicely, could be a scrolling roster on 3DS and take advantage of widescreen on WiiU.
Mario/Spinoff, Zelda, Sakurai (Kirby/KI), Pokemon, Metroid, Starfox, Fire Emblem, assorted game reps, Retro, Hardware, 3rd Party, Random/Mii.
Ganon(dorf) and Wario shown in Robot Chicken segment of Digital Event, Wario franchise has assist trophies.
G&W because of the Pacman trailer and the Amiibo image.
Ridley heavily teased, the Smash Direct trophy quiz.
Robin, Marshel, Shulk because Gematsu. Could have Chrom and Chorus Men, I just prefer this. Trophy quiz for FE.
KK Rool, Kremlings...
Vaati because Trophy quiz, adds a villain, compliments the Toon side, one of the most reoccurring villains besides Ganon(dorf).
Medusa is a stretch, fills the want for females and villains, the Dark Pit cameo in the Palutena trailer was odd.
Mewtwo "we're thinking about it" roster was likely already decided at that time.
Sceptile to replace Ivy and promote remakes.
Isaac has yet to be seen as an AT and may have made the jump like Little Mac did.
This is basically my best case / favorite scenario at this point. 39 + Mewtwo - 5 + 17 + Miis. Not very likely but I wouldn't complain with this. I could have did more in depth explanations but, have at it.
Edit: Plus there could be characters that are "clones" and share the slot with their "parent," like if Falco were to be cut, he could be a costume swap of Fox. Just speculating.