This game honestly is better that Wii u's version. Even if you have a Wii u copy of the game, you won't regret getting switch's version. First of all, all DLC is already downloaded so you don't have to download anything. Second there are new characters, a new power up, a returning power up, and new battle modes. Thirdly there are better graphics, and all track DLC is downloaded, and there is a 3rd charge boost when you drift. Overall fun game, and totally recommend you getting it.
I originally didn't purchase the game for the switch since I had it on the wii u. The kids still wanted to play online so I got it for the switch and it really did renew my interest in the game. It didn't feel a ton different but there were some nice graphical tweaks and the additional portability along with the larger online community was a bonus.
If I remember right, there really weren't a ton of differences. This is a pretty fun game... I think it's time to break it out again and play.
You know... I remember back many years... tons of people were asking for Mario Kart online. Now we have it... and no board members are playing together lol. It would be cool to start that up somehow.