All these threads are tangled in my mind, so ...
-a: I use this quite regularly for quick peeks at line and page
breaks without the trouble of writing a file and looking at it
in another window. It is certainly the option I type most--the
rest are buried in shell scripts.
separate maintenance. macro languages suffer from being almost
write-only. It's only a slight exaggeration to say that each
package requires its own special expert. I would favor separate
maintenance, with the maintainer filing a regression test.
The groff maintainer need only run all the regressions and
check with the package maintainer on failure.
It's helpful to ship a small bundle of macro packages with
groff, just as a small bundle of fonts is shipped. But specialties
(e.g. chem) would best be available for download from the groff
website rather thancluttering the distribution.
I would like to see font files as downloadable packages, too.