As explained in the issue MCPE-35026, the only way to transfer worlds from Minecraft Wii-U to the Switch is to do this : 

• transfer from: "Minecraft Wii U Edition" to "Minecraft Nintendo Switch Edition" (see: https://help.mojang.com/customer/portal/articles/2865993)
• then, transfer from "Minecraft Nintendo Switch Edition" to "Minecraft (bedrock codebase on Switch)"

The problem is that the "Minecraft Nintendo Switch Edition" cannot be found/bought anymore (this version was only digital and it is not available on Nintendo eShop anymore). In this case, as I just bought a new Switch 2019 to my kids for Christmas, there is no possibility to transfer their worlds .

I am a bit worried because I bought :

• Minecraft Wii-U
• Minecraft 2018 (bedrock) on Switch

... but I cannot buy the digital "Minecraft Nintendo Switch Edition" anymore. In that way, I have no possibility to transfer the worlds from the Wii-U to the Switch...

Is there any plan to allow the transfer : Minecraft Wii U Edition --> Minecraft (bedrock codebase on Switch)?