configuration files and PGDATA variable

I started to think about postgresql.conf.

Do you think it is a good idea, and how hard would it be, if postmaster and the
various utilities were able to read their whole setup from a postgresql.conf
file? Many UNIX utilities do this.

Think of this:

su pgsql -c "postmaster -C /etc/pgsql/mydb1.conf"

From this, postmaster can find all its settings in the config file. That way
you don't have to mess with startup scripts, environment variables, or anything
it just comes from the configuration file. Right now it is to hard to run two
different versions/instances of postgresql on the same machine.

Also, is there a real need to have a separate pg_hba.conf file? Couldn't
postgresql.conf also contain these settings?

I know this isn't of great concern to this group, but one of the things that
PostgreSQL does that kind of bugs me, is that it keeps its configuration and
data in the same place.