Ok, I'll bite.

What's your motivation? I've never heard of people wanting to write a new OS with the sole motivation of using a particular language, except for proof-of-concepts. (See below).

And to be clear, what is *your* definition of an OS? Cause an OS written in Perl has already been done: many moons ago, Simon Cozens created a Linux distribution consisting of a kernel with all utilities written in Perl. But that may not fit in your definition of an OS.