We've seen threads like this before, but it's still a relavent topic, and one very personal for me.
Nintendo's been doing good lately with their first-party IPs (Super Mario Odyssey, Breath of The Wild, Samus Returns and Super Smash Bros.), but there are still a few Nintendo IPs that need more love. A lot more love to be precise (F-Zero, Star Fox, Advance Wars etc.).
The one I think Nintendo needs to revive first and foremost is F-Zero. I know we have the FAST Racing games, but they're just not F-Zero. The track designs feel less outrageous, the cars look too similar to each other, and there are no quirky characters of any kind.
With F-Zero we got roller coaster-esque tracks, with awesome and diverse car designs, and fun drivers ranging from a bounty hunter to an evil emperor.
But which dead Nintendo franchise do you wanna see come back the most?