It turns out I had a couple of rc.d scripts in /usr/local/etc/rc.d
that were doing kldloads: rtc.sh and kqemu.sh - one of these was
causing the panic. It might be worthwhile adding to the world rebuild
doc a suggestion to grep kldload /usr/local/etc/rc.d and disable/
remove these services... Or, simply moving /usr/local/etc/rc.d might
also be worthwhile test.
I guess the trick here was not considering that user space apps would
be trying to do a kldload, and that calling upon a module that is
either missing in /boot/kernel or /boot/modules or resides outside
of /boot can trigger these panics.
Always the most simple of solutions that kicks you in the ass, isn't