If the arcanist manpage is shipped with the arcanist binary, i don't see where is the problem. Are you telling me the arcanist manpage content depends on the installed plugins ?

Is there a chance to have a man page for arcanist anytime soon?
Creating a manpage only requires running "help2man /path/to/arc -N -n "command-line interface to Phabricator" > arc.1". It can of course be run automatically when a new arc version changes its usage.