Lol, you mean majora_787?
But, anyways, one thing I'd definitely try is beating Classic with at least 10 characters. That's how you unlocked Young Link in Melee (as long as you beat it with an LoZ character) and Sonic in Brawl, I think they'll recycle that for Smash 4...
There really should be small cutscenes before fighting each hidden character, too. That'd be just epic.
It needs really fun, unique ways to unlock characters. Unlocking characters should feel fun and rewarding, not second nature like in Brawl. Maybe it could take a page from Mortal Kombat and have the hidden character appear very briefly give clues on how to unlock it before the round startes. I dunno, what are your thoughts?