I don't know if this is really good as an alternative as it is an idea for a final level of a SSB Story mode. But maybe take all those bubbles we see in the cutscene of the Great Maze and make them all recognizable locations. Each one representing a series that is represented in the roster of the game. Like have a world that leads to a classic Mario level, or one that leads to one set in Metroid. Something that combines what Melee did in the Adventure Mode with what the Subspace Emissary had instead of generic lands (Before Brawl released, I kinda hoped that the floating island was Angel Island as the location for Sonic to appear). SSB is supposed to kinda be about all the flagship franchises of Nintendo colliding with eachother, along with not so known characters from Nintendo's history and in the case of Brawl (And more then likely SSB4) a few 3rd Parties
I love it how when I played though the Subspace Emissary on Intense, this was one of the few levels one of my characters never died. I guess that's primarily because your characters get healed every twenty seconds in that level, but whatever.