Perhaps I'm in the minority but I've never understood the appeal of crossing over that many different properties. Now, I do understand the appeal of crossovers in general (I love Smash of course, as well as stuff like Marvel vs Capcom and Project X Zone), but when it gets to Goku vs Popeye vs Darth Vader vs James Bond vs Superman vs Scorpion vs Spongebob vs Shrek vs Mickey Mouse vs Maro and stuff like it's a huge turn off for me personally.
Perhaps it'd be petty, but that'd be what makes me drop Smash Brothers, because at that point I'd feel it'd be too far removed from what I like about the Smash in the first place. There is such a thing as "too much" in my opinion, which is also why while I'm generally supportive of third parties game characters, I also don't want there to be so many that they overtake the Nintendo characters in Smash.
I'll happily take another MvC, J-Stars, X Zone and what have you, but trying to crossover crossovers so to speak is where it becomes a cluttered mess.