Ok, it's too early to tell if it's completely sane, but I did just build a 
bootable kernel from the sept. 30 source tree I got from ftp.eecs.umich.edu.

Here's what I had to do (I know it's not *the* solution, but it worked for me,
hopefully, it will help the gurus figure this out...)

in src/sys/conf/files, the rconsole stuff is tagged as rconsole, not rcons,
and that seemed to be keeping the generic rcons (as listed in the files file,
from src/sys/dev/rcons) stuff from getting in my list of objects I needed to
build.  I changed the rconsole ocurrences in there to rcons.

in src/sys/arch/pmax/dev/rcons.c, change the name of  rconsoleattach() 
rconsattach()

in src/sys/arch/pmax/dev, rename font.c to rcons_font.c

in src/sys/arch/pmax/conf, edit files.pmax, go down to the rcons section
and keep the pseudo-device line, the rcons.c line, and the font.c line, lose
the rest of them.  Now change the font.c line to reflect rcons_font.c (as you
renamed it above).

run config.netbsd, cd to your ../compile/NAME directory, and 'bmake depend'

If you've previously tried to build, rm rcons*.o qv*.o and then bmake.

Thanks,
Mike