As you are probably waking up to hear right now, Pokemon X and Y was just announced. Its going to be for the Nintendo 3DS, and will have a worldwide release in October 2013. This game will also be the first fully 3D game in the series with both the human characters and Pokemon (and Pokemon battles) being in full 3D and no longer sprites.
However, contrary to what most of us were speculating, while the main legendaries for X and Y were shown off, there was no "generation mascot" shown off.
I think we will be seeing two major 6th-generation Pokemon in February (or maybe even the coming days/weeks):
1. A new evolution of Eevee (the Pikachu short for the 2013 movie is about Eevee's and they have been hinting a new Eevee evolution form)
2. The first major sixth-generation Pokemon that will likely co-star the movie alongside Genesect.
Since this new Pokemon generation game will be released in October 2013, there is a very good chance we will see Generation 6 Pokemon in Pokeballs for Smash 4. For comparison, Pokemon Diamond/Pearl was released in September 2006 in Japan.
However, with Black/White being old news, this effectively makes all the legendaries/promotional Pokemon for Black/White pretty obsolete. Zoroark is the only one left who is plausible for Smash 4 as a playable character. Genesect's chances are likely shot seeing as he most likely will be sharing his movie with the first major Pokemon of Generation 6.
It could very well be that the only new Pokemon added to Smash 4 is Mewtwo. However, it depends on what kind of impression the first major Pokemon of Generation 6 leaves on people. However, even then, its very likely that the roster will have been finalized by the time 2013 movie is released in theatres in Japan (July 2013), so a reaction from the fanbase would not be able to impact inclusion, but rather inclusion for such a Pokemon would either be through Game Freak/The Pokemon Company forcing Sakurai to include him/her/it or Sakurai thinking the new Pokemon would be someone Smash fans would like to play as (Sakurai likely has already seen it).
Overall, I hope this offers a lesson to Smash Bros. fans. Many of these people INSISTED that we would definitely getting a fifth-generation Pokemon, and yet many of them simply did not have staying power (the closest one to this was Zoroark, but even his popularity was but a mere shadow of Lucario's).
There is only one 6th generation Pokemon that will have a shot for playable status in Smash 4, and that will be the Pokemon starring alongside Genesect in the 2013 movie. We will likely find out the identity to this new Pokemon in February.
On a sidenote, looks like a Toise wig is going to be on the market soon.