Note to Arcandenik/Anyone that thinks I'm insulting this at him: I'm not, this post is generally about pokemon's representation in general. (And at the end somewhat about AT's)
Meowth probably won't get in. I won't comment on his popularity, because outside of Smash I think it would be greater than Jiggs at the very least (maybe even more so than any of the PT's individual Pokemon and Mewtwo as well) but given everything, I just don't see him getting in.
For one, I personally believe Mewtwo was cut from Brawl not due to time rerstraints, but rather the balancing of the roster, and that the reason he had some code was because they couldn't decide on him or Jiggs. We all know how this turned out, but I think its pretty clear that in order to get into another game, Mewtwo will have to be in another balance situation, or, will have to replace Jiggs directly, both of which probably won't happen. Its much more likley that the Pokemon roster will expand up to 5, and that the last spot there will go to a Pokemon in the newest generation. Thus I can only see Mewtwo having a shot if the max slots go up to 6.
Now for Meowth, this makes his chances of getting in harder due to the fact that he is clearly behind Mewtwo when it comes to getting in. He was never playable, and he really was never planned get in. The Pokemon roster would probably have to go up to 7 slots if he were to be included, which truly is pushing it too far. The only other opition I could see is if he latched on to a PT style deal, but I don't think that will happen either, as most people are gunning for another PT to have non-Gen 1 Pokemon.
^^ This is my feelings in a short summary, and you also have to all realize that It's not just all about pleasing the fanbase of smash, but pleasing the fanbase of each series. Why did lucario get in over Mewtwo? Because Mewtwo is freakishly awkward in programming (Half of his moves involved his tail) And because If you ignore all the other generations then pokemon fans won't be the happiest of people, considering since It's an RPG It moves from time to time.
Thus why 5th gen or the next generation by the time Smash 4 comes out is considered a "Shoe-In" Because of fans who just got into the series or so. Really; If you think Jiggs/Pika/PT Are getting cut for what essentially is another 1st gen pokemon, you're out of your mind. The most recent gen is apparently shoed in in sakurai's eyes - Anyone who screams "LOL TIME CONSTRAINTS" Really needs to realize that most time on the game was spent on SSE And Online as stated in interviews and that the dev team themselves said they don't spend a lot of time on characters + The fact the roster was decided in late 05.
With the knowledge we have; We know four reps (PT/Pika/Jiggs/Someone that doesn't rep 1st gen) Leading to 6 movesets and you still have Lucario, Mewtwo, and the apparent idea of sakurai considering Plusle+Minun (Tho, I'm doubting this too), and going by the fact he axed 2 Poke to fit in 2 new poke; I think It's safe to say there's most likely only one more slot for Smash 4 (Balancing + The dude still needs to fix Jiggs at least some
)...
Now let's say Sakurai feels First gen is worth of representation - You really think Meowth will get in over Mewtwo? Uh...
And If somehow pokemon gets 6 Slots and EIGHT Movesets, then why should meowth be deemed as worthy when It's a FIFTH First gen?
And that's a long explination of how I feel about pokemon's representation; Wasn't only aimed at the whole meowth thing.
Edit: If you guys are going to suggest a second PT, at least say something about it that stands out originality wise, or you're just essentially adding another PT (Since It'd probably have starters or something) Just for the sake of having more poke playable (And...At least Nine movesets @.@)
Edit2: Tho I'll agree with n88 on one thing at least for sure about this; Meowth still got a rather good amount of requests on various forums, but his support after he was confirmed as an AT Is long dead. He really had his chances mainly in Melee/64.
As for my opinion on Assist Trophies...
While people are going to bring up the whole thing about pokemon, It's still two different cases. AT's Are split between almost every other series in smash; It doesn't really lower there chances or bring them up; Because If there was anything that did so, that was already done in the first place. (IE Andross is not in because he's awkward to program)
So really; I believe we'll see some become playable in the next game...Few, but some. (ISAAC PLEASE?)