I think that if Nintendo was to introduce a second crossover franchise, it should be a cozy game of some kind. Not just because Nintendo's only active cozy franchise is probably bigger than Zelda at this point, but also because it would allow for character interactions; a huge character pool; a better embrace of Nintendo's mostly-kiddie library than Smash's perpetual "No guys, Kirby's just as cool as Kratos, don't take my lunch money" phase; and also just be very sweet.