Nintendo is almost certainly the one providing the funding for this game.
Sega is broke and can only finance Sonic games and little else.
Platinum is a small indie studio that needs a "sugar daddy" to pay their dev bills.
It's Nintendo guys. Get over it. The moment Nintendo spends even $1 in development on this game (let alone probably the entire budget) is the moment it's over. It's never going to be on a non-Nintendo platform.
Nintendo should just buy out Sega's IP period. Probably can be had for cheap at this point, Sammy would probably be happy to wash their hands of it.