^ Which is also why I think that if Raichu is to be included, Pichu should as well.
In the older thread, I made a suggestion of a PT / Pikachu combining sort of character, where you start out as Pichu (assuming you take 3 stocks) and after gaining 'happiness' in this way; beat the first stock of the opponent without losing yours, you evolve into Pikachu. Who again, could evolve into Raichu upon finding the Thunder Stone, which would appear as an item Pikachu needs to grab. Opponents in return could also get the Thunder Stone and either throw it off stage, or throw it at Pikachu.
There'd also be the possibility to play as Pikachu alone but you'd have to press at Pikachu specifically, much like Zelda / Sheik and the Pokemon Trainer's Pokemon.
It's very unlikely to happen, and I feel that if they do this for Pikachu, why not do this for Pokemon Trainer as well? Options: 'Standard Pokemon Trainer' - Squirtle, Ivysaur, Charizard, 'Fire Starter Pokemon Trainer' - Charmander evolving into Charizard, 'Grass Starter Trainer' - Bulbasaur evolving into Venusaur and 'Water Starter Trainer' - Squirtle evolving into Blastoise.
Igglybuff - Jigglypuff - Wigglytuff and Riolu - Lucario could also work, but it might be too much work. Just add in standalone Mewtwo, Lucario and a 5th gen rep and Pokemon would be fine. But really, it all depends on how many characters are to be added.