I'm with you. If this isn't coupled with at least a P5 port (we'll know by the 25th if it does), it'll really rub me the wrong way, just like Snake's inclusion does.
You know what makes Marth's down air spike feel good?
His Nintendo roots.
Jokes aside, I understand how character association can enhance your enjoyment of a character, but that has nothing to do with which console they were on, and everything to do with the game they're from.
So if someone is lacking that with Joker, the problem is that they haven't played it. Not the name of the console you played it on.
Smash is a celebration of video games, and if someone only plays Nintendo games, that's their prerogative. Though I think they shouldn't let that get in the way of their own enjoyment of a character either. I had never played Fire Emblem when I first tried Marth, and I still loved him. And you should certainly not punish everyone else for a reason like that. People who never played Final Fantasy 7 loved Cloud. And I'm sure the same will apply to Joker, his stage and the music.