aaaand the floodgates have been opened for DLC. Nice to see Mewtwo back, hopefully he's not terrible like in Melee.
I think Wolf has a strong chance as DLC since there's a new Star Fox on the way, so I can see them doing him as DLC to advertise that. Lucas I think is pretty much dead since Ness has his specials as customs, and as a rep of a Japan-only game of an incredibly niche franchise, I don't think DLC for him would sell too well.
...It had a third game because people WANTED a new KI game. The original KI was a cult classic just like Earthbound; that's how it got into Smash to begin with. While Dark Pit is a terrible addition, KI being more recent and successful than Mother justifies it getting more reps, though not to the extent it has I'll agree.