Dillon isn't as Third Party, I think.
Published by nintendo.
Here are the eshop reps that were published by nintendo:
Dillon (Could be a playable character- considering Rosalina's playstyle it's not too far-fetched that his down B could be building a small tower as a stand, which would officially make him the coolest character ever. Although if they don't play with his gun towers, he would end up way too similar to sonic. I think it's kind of far fetched for him to get in, though.)
Pushmo guy (I think this has been brought up before, but he would be THE BEST as an assist trophy or a stage. Can't see him playable.)
Sakura Samurai (Would be a pretty boring playable character, but perfectly fine for an assist and I think I brought up before that this game is WAY too beautiful not to get a stage.)
Harmoknight (Could see him being playable, there's certainly room for a move set, particularly if they're willing to let him summon his friends. Could also make a good stage/assist trophy.)
Ketzal's Corridors (Maybe an assist trophy, kind of maybe a stage? This one's hard to work with. A shame, since the game is really good.)
Although, for the record, I don't think it's out of the question for a 3rd party eshop rep to get in, especially one that's nintendo exclusive like mighty switch force. If you're a small developer and you get a call from nintendo asking if you want your ip in Smash Bros, you would be fucking insane not to say yes immediately. I mean, talk about free advertising...