Is there any reason why Windows or at least Cygwin isn't supported? Much of the time, the whole point of SSH for me is to connect to a Unix machine from a non-Unix machine.
The code compiles under Cygwin with not too much effort -- the current master may compile. The big problem there is you don't really have a good UTF-8 terminal, but you're welcome to use it. If you know how we can best package the software for Windows or Cygwin users, we're happy to take a patch. (github.com/keithw/mosh.git)
Mintty, badly. The first test gives no hat (or I just can't see it). The second causes it to get stuck in heiroglyphs. The third doesn't work correctly either. It looks like it prints xyz correctly, then jumps to the second line on screen and then continues from there.
The "cygwin bash shell" which uses cmd.exe does the first test correctly but similarly fails on the others.