I think letting you set the irq/port's (ignoring the mechanism) misses
an important point.  Would a naive user be smart enough to iterate
thru all the possible irq's (and possibly ports also) to find
one/several that will work for his machine.  The current scheme masks
off irq 10 by default because that is bad for some people.  Well, irq
11 is really bad for me and the new sony VAIO seems to not like irq 9
and irq 5 is often sound and ...

Let me suggest something different/stupid.  Could we let the boot
program pass in the "name" of the machine.  The kernel would have a
table that adjusts whatever parameters are necessary for that machine.
These parameters could be: allowed irqs/allowed ports/whether sb uses
irq 5 or 7/whether "the media inserted into a floppy" bit is inverted/...

We could also consider generalizing from machine name to (optionally)
a list of features like, enable apm.  This way I might be able to use
a generic kernel on laptops and desktops.

A final part of the "design" would be to that when a "biosboot.sym" is
installed to store with it a set of parameters that it is to use.