Default libpq service

A while ago it was speculated that it might be nice to have a default 
service in libpq's pg_service.conf file that would supply missing 
connection parameters if none are specified elsewhere, so users could, 
say, set the default server host in a configuration file instead of 
environment variables.

The precendence would be like this: explicit specification, service (if 
explicitly specified), environment, (new: ) default service, 
compiled-in default (e.g., for port).  (Or maybe the default service 
before the environment?)

Comments?  Better ideas?