Whoever hasn't played this on Wii U and picks it up on Switch is in for one hell of a good game. But even with the proper battle mode, which should have been in MK8 (no excuses), with no new GP tracks added, I'm just not going to double-dip on this one. And it kinda makes me worried that MK9 will be a few years away on Switch, as I fear they may use this as the sole MK game on the system. It just wouldn't be right to have two MKs on the same system, with one potentially pulling online users away from the other.
The only thing I can think Nintendo might do is produce a couple more DLC packs like they did for MK8 on Wii U, but even then, I would be hard-pushed to rebuy the game and buy the DLC on top of it unless the game itself goes pretty cheap.
Don't think Nintendo has done the right thing for those that invested heavily into the original game, personally, but newcomers will get something pretty awesome.