@pry In the paper I linked up on top, if you can get over the snarky remarks ;), Backus goes on defining a few alternative futures, one of those is something like a stack machine.
But there's a lot of different possibilities, the lisp machines don't really do anything special but are still worth looking into: http://wiki.xxiivv.com/docs/memo528_cadr.html
You might get a kick out of the LispKit books(SECD-style), or the BQN VM(APL-style):
https://mlochbaum.github.io/BQN/implementation/vm.html
@pry alternatively, you can imagine a Thue-like computer where its only instruction is string replacement, and how that might look like.
http://wiki.xxiivv.com/site/thue.html