How about a tool that would generate a prototype disktab entry from
   MODE SELECT data?

That *still* doesn't deal with the partition info, which is the
primary use of disktab to begin with.  You can't divine that
information.  (Hell; you don't even need a label if all you want to do
is access the raw disk.)

I, for one, have never used disktab under NetBSD.  But that's another
subject.