The fact we mostly have third parties honestly. I thought we;d have maybe 3 or 2 and be done with it.
Joker kind of made me believe it would be mostly 3rd-party. The reason being, if they had only 2-3 third party they would have chosen better.
If you limit to 2-3 third party, it would probably have just been Steve, Sora, and perhaps a Banjo or Hero character. That way you reach the largest audience.
However, I can see your point. Great post. I think the reason first party has been abandoned by even many of the Smash fans on the want list is that it has been done to death. There isn't many iconic first parties out there. You are getting into niche series and side characters. I would say that Dixie Kong, Impa, Toad, Waluigi, Bandana Dee, and Chorus Kids are the most likely ones left out there.
However, I can see your point. Good post.