I just want to boot into a Lisp repl and go from there.
It would be great if the Lisp dialect/implementation that is bootstraps the bootable Lisp would also be written in Lisp instead of what I've seen from most bootable Lisps in C or Assembly.
There is PicoLisp PilOS: https://picolisp.com/wiki/?PilOS
Also, uLisp is kind of related: http://www.ulisp.com/
But honestly, I would just install the GNU Guix System (and perhaps use StumpWM or emacs+EXWM) or install Mezzano inside a VM.