Probably not as it stands?
Right now the whole thing is built on a couple of underlying frameworks: .NET core, wasmtime, and FNA. All three of those are likely to pose issues with porting to the Wii, not least of which is FNA - as it is an open-source implementation of XNA which mainly targets modern rendering frameworks (D3D11, OpenGL 3.x, Vulkan, etc), using lots of features that just wouldn't work on a fixed function pipeline like the Wii. I get the feeling that a dynamic JIT compiler based runtime (WASM) may also pose a few issues.
That said, it *may* be possible to take a different approach - it could be theoretically possible to write a framework for the Wii which exposes all of the same functions as the Dreambox WASM host does, and then use maybe something like wabt to translate a Dreambox WASM game into C, and statically linking it with the aforementioned framework and compiling it for the Wii. Lots of extra steps & complications though.
I had at one point considered seeing if something like this was possible for the Dreamcast, but decided against it as none of the compressed texture formats would be supported so it'd be of limited utility. I also have made a grand total of $6 on Dreambox ever so it doesn't leave a whole lot of room for experimentation on niche things like this ;)