Then Sony would have to make PS All-Stars vs. Smash Bros. Which would follow All-Stars' playstyle with supers.
Both games could be sold on both platforms. Everybody wins.
This is never going to happen between Sony and Nintendo but it will and is happening by fans of both games. Some dedicated guys are shooting for a super smash flash style of game with Playstation All stars fighting against Smash Brothers. Its not done yet but check it out here http://pastadium.forumotion.com/f14-project-axis
No....just no lol. how would the rivalries work? it would be awkward having a characters like say Mario and Kratos be rivals. most of Nintendo's cast are silent protagonists, this would make the rivalry cutscenes VERY bland. also, Nintendo would have to double dip from their franchises to make up their side of the roster.
both I believe are exclusives to different consoles