The Wii U version of Minecraft was basically put out to pasture when it wasn't included in the “Better Together” cross-play update. In summation, any version of the game that retains the “Edition” moniker will be limited to its own platform, while everything else can play together. Notable exceptions include PS4, Vita, and of course, Wii U.
This led to a lot of people naturally upgrading on Switch (where Better Together works), but they had to leave their save files behind. Well, that changes this week, as Nintendo has implemented a cross-save transfer from Wii U to the newest Nintendo generation. Just load the game up on Wii U, select your save, select transfer, then import it on Switch.
I never really got into the Wii U version (I kept playing Xbox One and only dabbled in the new Mario sandbox), but if I did, this would be a nice concession. Provided that you're okay with eating the cost to upgrade of course.