The project running on browser is not the main point. It can run standalone, and is mostly used to run old games that no longer work well on modern hardware / windows. Heck you can even use it on Linux.
I think the coolest part of the project is that it makes wine very portable though. Boxedwine seems like it could run on android as well for example.
Basically this project is a Linux emulator but rather than exposing libc APIs it exposes Win32 et al via WINE.
Pretty neat idea but comes with all the usual caveats of running Windows software on WINE plus all the new caveats of running C++ in WebAssembly.