2. Emacs already contains bat-mode.el which explicitly states that it is
for editing Windows specific scripts and also includes functionality
to execute those scripts using the proprietary interpreter:
Many years ago I wanted to install a tiny fix to work around a difference between cmd.exe and 4DOS/4NT (a proprietary command shell for Windows), and was told not to. IIRC, it wasn't even a change to bat-mode, but to one of the .bat scripts used back then to build Emacs on Windows. Something similar happened with CVS support vs CVSNT (it was a question of adding a non-standard parameter that CVSNT required to be silent).