A similarly amazing machine that IBM's System/38 learned from a little bit. Somebody posted a link to an emulator but honestly I don't want to dredge through that. Like you said, a modern system that reimplemented its best attributes without the limitations or baggage would be nice.
Mainframes are complex enough that there's rarely projects to implement them but there's lots of work on safer CPU's. See crash-safe.org's early publications for a CPU that combined Burrough's-style checks, Alpha ISA, and functional programming at system level. Given stack preference, you might like these:
