Zelda, Metroid, Kirby, Star Fox, Smash Bros. These are probably the ones that makes the most sense for a movie. However, I doubt some of these would fit with Illumination's style. I would love to see a Zelda movie made by Ghibli or surprisingly a live action might work if it's Zelda or Metroid (I know). I hope Nintendo would explore different studios and options other than Illumination.
Splatoon, Fire Emblem, Animal Crossing would be a nice tv series, maybe an anime adaptation since there's already a manga about them.