It took me a while -- three months -- to realise that I hadn't seen one way or the other whether the problem with
abstract internal members a couple of levels back up the inheritance tree (that thwarted my previous attempt back at the end of last year) had been fixed in the May CTP.
The cmdlet code is unchanged in the Feb 2010 (v 184.108.40.206) CTP.
Well, I can report that building
now actually succeeds. So there should be nothing stopping us writing a full PowerShell snap-in in one F# assembly.