So, I've gotten myself what is either a wonderful contract or an awful one.
Three people have tried and failed to achieve this.

The subject of our discussion is a Soekris systems box - an N4521.  AMD sc520
single-chip processor, some memory, two cardbus slots and a CF slot, one
serial port, two ethernets.

The goal is a purpose-built box that fetches data over a serial port and
makes it available somehow over wireless LAN.

Two things would make this much easier:

1.  Is there a sane way to make NetBSD run *totally* headless - no
console device?  The only serial port will be used up by something else.
(I can work around this temporarily, but in the long run, it's the best
thing for me.)

2.  I seem to recall people doing read-only boot filesystems; is this as
easy as I'd guess it would be (union mount an mfs filesystem over / early
in the boot)?

Feedback and suggestions welcome.  I'm aware that people have FreeBSD running
on this box, but I have faith in NetBSD's ability to DTRT on weird hardware.
I am particularly pleased to note a driver for the SC520 - thanks, Mr. Thorpe.
I owe you a beer.

-s