It would be nice to finally fix ad_conn url for host node mapping cases.
It's been a couple of years since I've been messing with host node mapping.
Apparently site_node::conn_url isn't a direct substitute as I mentioned. I'm terribly sorry about spouting that without re-checking.
site_node::conn_url is a proc for building urls that work when ad_conn url breaks for host node mapping.
One can use site_node::conn_url to generate urls that work with or without hostnode mapping, so that a host node mapped site works from the main domain as well.
Using site_node::conn_url is really useful when the main domain has a ssl/https setup, because the site can switch back and forth between http/https without generating a security warning or changing the display templates. You can direct a user to login via https and then switch them back to http on the hostnode mapped subsite after login. The UI flow is smooth.