What would be the challenge to write OS kernel in Lisp? Just X86, for the sake of umm simplicity, something like xv6: https://github.com/mit-pdos/xv6-public

Yes, I've read about Lisp machines. Sounds like a super expensive machine only accessible by big-budgeted research companies.

Most of Lisp folks on the net talk about how homoiconic language is elegant, or how REPL makes development faster, or how useful Lisp is for automatic theorem prover etc etc but very rarely I see Lisp folks talk about system programming, unlike C/C++/Rust folks.