Burroughs MCP still exists, so I am not sure how true your statement that it was "prematurely abandoned" is. Burroughs became (through a series of M&As) Unisys, and Unisys still supports MCP and is updating it with new versions. It runs on Unisys Clearpath mainframes. Unisys has moved away from their distinctive physical hardware to software emulation on an x86 platform. x86 has improved so dramatically, that even given the emulation overhead, it still is faster than the old physical mainframe CPUs.

There is also an emulator which runs an old (1970s) version of MCP, not the current (2010s) version - http://www.phkimpel.us/B5500/