I don't think Nintendo will be launching with a 2D Mario again any time that soon after Wii U. It's not like NSMBU was a bad game, it's probably the best NSMB game by a fair margin.
I mean I think 2D Mario just isn't great for a launch game. You want to show off the system with launch games, and 2D doesn't do that.
I would certainly expect a 2D Mario on Switch though, cuz it'd be insane if they just skipped 2D Mario on a system with Switch's user base and only gave us the rather mediocre old ported game from the WiiU (maybe its not mediocre but the "New" formula just feels old and stale at this point, hard to say which, but regardless it wasn't a particularly great game IMO).
2D Mario would be a 20 million seller on Switch so I'd be shocked if they didn't have one in the late stages of development right now. 2D Mario as the big holiday title this year makes perfect sense unless they are gonna do like a surprise release to coincide with the Mario movie this Spring. 2D Mario on Switch and 3D Mario for Switch 2 launch makes a lot more sense than the other way around (which I just mention cuz I've seen some people saying they are hoping for another 3D Mario on Switch).
But yeah, like you say the epic games are the sorts of things that should be launch games. MK9 and 3D Mario make the most sense, because its obviously not going to be Zelda since we're about to get a Zelda game and Smash Bros just seems unlikely. Metroid Prime 4 could be a launch game as well if work on it was just going soooo slowly that they at some point decided to target the next-gen instead but I'm hoping we get Prime 4 on Switch this year, well before any successor launches.