Seems too early to be a new main game announcement. Got to be either DLC or a spinoff, right?
It's a very longshot, but I'd love it if they announced some Pokemon stuff coming to Mario Kart. They just announced a new MK DLC and only 1 track was revealed, also confirmation that they're willing to add characters. Seems unlikely, but Pikachu in MK with a Pokemon themed track would be amazing!