I find this a fascinating subject. But there seem to be so many dead ends. Here is a page I found some time back with Lisp OSes. There are many dead projects mixed in if I remeber correctly.
This one seems very interesting.
"The Movitz system aspires to be an implementation of ANSI Common Lisp that targets the ubiquitous x86 PC architecture "on the metal". That is, running without any operating system or other form of software environment. Movitz is a development platform for operating system kernels, embedded, and single-purpose applications. There can potentially be several completely different operating systems built using Movitz."
Common Lisp on the metal would be an example of Common Lisp as Assembly, no? Project hasn't been posted to in years though.