I work with an old DEC guy who co-wrote a book about the BLISS compiler back in the day. He thought it made a much better "portable assembly language" than C.

He also likes to talk about the binary compatibility on VMS; e.g., VAX binaries that run unchanged on Itanium. Unfortunately, that commitment to compatibility has wavered a bit since HP offshored VMS maintenance. We've had to work around some breaking changes recently.

If I'm understanding these slides correctly, AMD64 VMS would require recompiling VAX, Alpha, and Itanium applications from source. I kind of see a chicken-and-egg problem: application vendors won't port without demand, and customers won't adopt without applications.