That wasn't the point. The point is that most of the field abandoned stack hardware for register hardware, upon which all sorts of software paradigms are implemented.
I've read Koopman; fascinating stuff. Really solidified my understanding of the use of multiple stacks in Forth-like environments.
But I think it's instructive that none of the commercial architectures he describes (from 1989) have a contemporary descendant (although I think you can still get the RTX 2000 as a space-rated special order at an astronomical unit price). I think that tends to support my premise.
The 8087 was basically obsoleted by register-based SSE2 and SSE3, and as I understand on x86_64 the vestigial 8087 op codes are decoded microinstructions executed by the SSEx unit. And the descendant of the B5000 (now called Unisys ClearPath) is a VM running on Xeons; they stopped making stack-based MCP processors in 2015 or so.
