A not-so-close approximation to using a Lisp Machine these days is to use the GuixSD distro. It features a package manager, init system, and initial RAM disk all written in Scheme. Combine that with Emacs, the guix-emacs extension, and, if you are so inclined, a Lispy WM like StumpWM and you have a system where a large number of critical components are implemented in Lisp.