This might be a bit adventurous --- there could be
another use for "config": configuration of loadable
drivers. In this case, the config file would only contain
a description of the devices to be included in the
loadable module.
(I played around with it beginning this year. It worked
in some degree, but I didn't continue after the change
in the config file format.)
No substancial changes to "config" were necessary
for this - only some flexibility to add:
- Allow to specify the compile directory. (This is
  covered by your proposal.)
- Don't insist in having exactly 3 "dev_defs" descriptions
   (in "gram.y"). For this purpose, 1 is enough.
- "failsave" option: don't error out on missing "maxusers"
   or "maxpartitions"; weaker crosschecks for un-connected
   devices.
- create alternate names for the config tables in "ioconf.c"
   to avoid namespace collisions.

Just some ideas...

best regards
Matthias Drochner