I've been reading the Super Smash Bros. Wiki, and apparently Meowth (along with Pit, Peach, and a few others) was considered for the original SSB, but was cut due to time/budget constraints. I'm glad I'm not the only one that thinks he'd be awesome, and I'd love to see him in Smash 4, filling the role left by the likely-leaving Lucario. Bonus, since Meowth has a bit of a legacy (being a Generation 1 Pokemon and a major player in the anime) I could see him sticking around.
Sakurai has said he'd like to develop Smash 4 for 3DS and WiiU, and that the two games would have some sort of connectivity. Now this I think is a very cool opportunity. WiiU can have the big, epic grand Smash 4, with a huge roster and such, and 3DS Smash can have a smaller-scale more "personal" experience. What about this: Maybe 3DS Smash is a sort of "Heroes and Villains" edition, with a cast that looks something like this:
Mario
Bowser
Donkey Kong
King K. Rool
Link
Gannondorf
Samus
Ridley
Kirby
Dedede
Fox
Wolf
Pikachu
Meowth (Yeah, he's officially part of my list of characters I want in Brawl now)
Pit
Medusa
Capt. Falcon
Samurai Goroh
Little Mac
King Hippo
Basically, any Nintendo series with a Smash-worthy hero and villain is represented by their respective hero and villain. Of course, this would leave some classic smashers high and dry, like Mr. Game and Watch or even Yoshi. I don't know enough about the Advance Wars or Fire Emblem or Mother/Earthbound guys to come up with a respective playable villain, but if they have one, throw 'em in! I think this could be one way to make the 3DS and WiiU Smash Bros. games unique from one another. Being a handheld/portable title, having a smaller cast list makes sense: this is Smash Bros. Lite, on-the-go. Connectivity? If your WiiU wirelessly communicates with your 3DS copy of Smash 4, you can unlock some of the exclusive characters from 3DS for use in WiiU, and vice versa.