The VM, as John Dyson has pointed out in the past, is not irretrievably
architecture specific. I don't believe there is a technical issue at
all... I have had FreeBSD's VM code working on Alpha and, more recently,
PPC hardware, with only minor changes.
I have also heard that, it is not 386 specific, but rather "FreeBSD
specific", you're right, but I haven't heard of anyone using FreeBSD's
VM under NetBSD (did you?).
It is true that the interfaces in the VM system have changed (and are
therefore FreeBSD specific), but those interfaces are part of the
improvements associated with the VM code. Changing the interfaces
isn't all that difficult, and the hardest part about a port of the
VM code is likely the pmap module changes. One really bad thing
about the original VM code is that the pmap code is called lots
and lots of times. We have mitigated that significantly.
Frankly, it is likely that a VM system that performs as well as
the FreeBSD VM code (and I am not making any relative claims here --
the other *BSDs are making some improvements), is going to require
interface changes relative to the original Lite/2 code.