Virtual Boy would be a sweet retro/wtf/hardware rep, though maybe too similar to R.O.B. and I think that commercial where it has legs and is a menacing robot thing was only in america so the idea might not hit sakurai to portray the system that way. It did have the first real instance of mario tennis on it and with aces coming out... could be a good time to reference the VB.
Always hard to guess the retro/WTF/hardware rep... game and watch, R.O.B., Wii Fit Trainer, and duck hunt were all surprising characters with only duck hunt really having anyone online pushing for it (though i think most didnt think itd actually happen, me among them, glad it did though).
This time people are far more keen on trying to figure out what we'll have sakurai throw at us but theres far less to choose from I think the possibilities are Virtual Boy, Diskun, Hanafuda cards/daitouryou, Labo man/Labo Robot, Gameboy... am i forgetting any? Seems like we dont have many left as some are just "make the console alive as a character", labo might be way to new, and the hanafuda cards might not be "vdieo game" enough for sakurai to include. Its always a tough one to guess at and even now when we expect it, its still tough to predict.