>>4
RISC-V and ArmV8.5 both have tagged memory extensions. I think that's really rather exciting from the perspective of future lisp-machines.
Some of the stuff you mentioned is outlined here: http://metamodular.com/lispos.pdf
I think it's pretty cool and I have some ideas on the topic, though I can't really start in earnest until current projects are complete. At least some of what made the LISP machines possible was simply the amount of money thrown at them, and the level of talent which ended up working on them. It was the early google of its day in a lot of ways, in that hackers would happily want to work on the development of LISP machines. Now, it's a bunch of oddballs on obscure web forums.
Oh well, if LISP is really as powerful as we think it is, and it really gives a hacker the leverage we think it does, then why shouldn't a bunch of oddballs on obscure web forums be able to build their own LISP machine? If it can't be done, then was it worth all the trouble to pine over it? And if it can, then we should do it.