First thought in my head: A straight HD + online port of GX would be a mess. 30 cars snaking madly, lagging, and pinballing off one another nonstop? Might be better to stick with Dolphin.
Now, for my elevator pitch:
-Make a course creator the centerpiece, a la Trackmania. Nintendo curates the best ones and rotates them into the main GP and online modes, along with a mix of new and classic tracks. Every couple months, kick off a new "season" with new courses, forcing players to experiment with different and offbeat builds to stay competitive.
(Of course, include a "free race" mode where any/all user-created and downloaded courses are playable too. Knowing Nintendo they'll probably make it friends-only or some nonsense, but eh.)
-Players can acquire car parts and mods from 4 sources: in-game shop, Pokemon-style "events" where rare/exclusive parts are given away, trades with friends, and as "trophies" from destroyed rival cars. (Parts 'lost' when your car is wrecked can still be "rebuilt" with in-game credits, so no perma-loss. But maybe throw in a "hardcore" mode where's it gone once, gone forever? )
-Graphically...how about a throwback to the style of the SNES comic, with a slightly heavier/inkier look? And title it "NEW F-Zero Grand Prix" or somesuch.
-3DS only at first, glorious 1080p60 WiiU port if it succeeds.
GAF, your thoughts?