Well, I can think of a couple of problems:
- The microvax I cpu didn't have hardware support for double precision
  floating point. (Which means, live without a lot of utilities or write
  emulation code for it. Yich:-)
- As mentioned by someone else, it uses q22 bus memory, which means a maximum
  of < 4Mbytes and with most boards being 512Kbytes (I think there was a 1Mbyte
  board, but I'm no sure), you probably can't get 4Mbytes in the box.
(Even if you get past 1 and 2, it's doggy dirt slow..)

I'd suggest you find a MicroVAX II or III motherboard and memory card and
use them to make it into a machine that will run NetBSD ok.

Good luck with it and have fun, rick