Can the py.exe launcher handle a UTF-16 shebang? (I'm pretty sure Unix
program loaders won't.) That alone might be a reason for strongly
encouraging ASCII-compat encodings.
That raises an interesting question about if py.exe can handle a
leading UTF-8 BOM. I have my emacs-on-Windows configured to store
UTF-8 without BOM, but Notepad would put a BOM when saving UTF-8,
last I checked.