It's not buggy at all -- I've been using it extensively since it was first available and have not run into a single issue.
* Swift runs natively on Ubuntu, however on WSL only the compiler works. If you try to run the REPL it will crash.
* Emacs, slow start, seems to work for simple editing. Crashes when you try to install a package or when you try to list the available packages.
So there certainly are some bugs.