When it comes to crossover titles, Project X Zone is pushing the boat out by merging three universes: SEGA, Capcom and Namco Bandai. One issue that won't affect this game is a shortage of characters, with plenty of them lined up already and more just announced.
Famitsu has revealed (via Andriasang) that Tron and Kobun/Servbot, from the Mega Man franchise, will be involved. SEGA is joining in with Bahn from the Saturn's Fighting Vipers, while Namco Bandai is including characters Reiji Arisu and Xiaomu from PS2 crossover title Namco x Capcom.
It's also been confirmed that the opening song will be Wind Wanderer, performed by Yoko Takahashi. If it's as good as the music we've heard for the game so far, then that'll be worth a listen.