Event that cut character has more importance and popularity in Pokemon than Meowth does. Besides there are so many cooler and unique Pokemon that are more beloved than him anyway.
I just really don't see why Meowth is even considered an option. Him being important to the Anime doesn't really put him over Zoroark, Genesect, and others. Realistically Smash 64 was his only chance.
Genesect is more popular now because of the Movie.
And 95% of Pikachu's importance comes from the anime.
Originally Ash was going to have a clefairy as a starter, if this plan went through, Clefairy would probably be in Smash Bros instead of Pikachu.
And also, I don't see a Unova rep very likely considering that in Brawl a Hoenn Pokemon didn't get in because Sinnoh just rolled around.
EDIT: Meowth does have some importance outside of the anime, there was going to be a GC game called Meowth's Party. And he is also heavily featured in some spin-offs. The same games that center around Pikachu.