F-Zero would be a great alternative to Mario Kart. I doubt it would eat into Mario Kart sales. Mario Kart always sells 20 million plus and is a chance to hit 50 million on the switch at this rate.Speaking of dead franchises, I can bet money on continuing to not see anymore F-Zeros since Miyamoto doesn't want copy/paste sequels. So if he can't find any good new ideas then we have to stick with the N64 and GC games.
Id really like to see a new Star Fox game. Like an actually good sequel to 64 instead of an ok sequel like Assault or a boring reboot/remake like Zero.