I believe that games like the Kart and the Party series will always have mario-only carachters, being them "super MARIO kart" and "MARIO party". Super Smash Bros does not have MARIO in the title so it is not limited to mario carachters only.
There may be Kamek, Waluigi or even Daisy, but not Link, leave alone Samus!
so, my dream roster is... the same of the GBA version.
there will be secret tracks (maybe the original NES ones) and there MIGHT be secret carachters.
the real challenge is guessing the
NEW SECRET FEATURE
Nintendo is keeping secret.
They are not revealing it now because they are afraid that other kart games will copy it.
Cele the Ref