I had an idea last night and thought about it and it would make sense. I was watching Gamexplain's Mario Party 10 Discussion and at one part they tlked about Spike being a character because of the background he has which is similar to all other playable characters.
So I think in a future DLC pack there are going to be three characters available which are:
Obviously I don't know the tracks and vehicles but I think this will make a pretty unique DLC pack like the rest.
Also, I do hope they bring a DLC pack with Mario Kart veterans such as:
I also hope they bring in some new characters, which were fake leaked early on after the game was released, which were:
Professor E Gadd
Hammer Bro (not in leak just like the idea of him being playable)
and a few other Mario Kart veterans which are listed above.
I also have a feeling that Nintendo will release at least another two DLC packs with 3 characters each like these ones, because they would fit nicely going down on the right hand side of the roster.
Also, after that I have a feeling that Nintendo will release a DLC with more Battle modes and actual arenas.