Previous efforts got killed because the off-brand hardware, especially the CPU's, were never as fast and/or cheap as Intel/AMD. They also required new tooling and such most of the time. This happened to LISP machines and apparently Azul's Vega's as they're pushing SW solution these days. So, that's my guess.

Most general I saw was in a Scheme CPU where the designer put the GC in the memory subsystem. The Scheme CPU would just allocate and deallocate memory. The GC tracked what was still in use on its own in concurrent fashion. Like reference counting I think. Eventually, it would delete what wasn't needed. Pretty cool stuff.