Hey, sorry late reply is late. NantenJex is staying at my apartment this week, so I've been pretty busy.
Top contenders? It really depends on a lot of factors.
The first, is Sakurai coming back?
This is something we discussed
with NintenDaan awhile back.
Depending on that answer, it will influence what characters and how many we could get.
The second factor is if
the rumor is actually valid (so far,
it's not dead). The rumor states it'll be a director's cut, and featured limited new content (Ala
Mario Kart 8 Deluxe).
Smash hasn't been shown off yet, but with the amiibo listings, and looking at the history of
Smash announcements, it seems very likely it'll be announced at E3.
With that, I think Ice Climbers, Wolf, Inklings, King K. Rool,
Dragon Quest character, Takamaru and a
Rhythm Heaven character are all contenders. It depends on how many characters, and who is working on it. We discussed
it here with Roger's Base.
Anyway, let me know if there's any particular questions you have!