Dispatch has a plugin system: https://github.com/Netflix/dispatch/tree/master/src/dispatch/plugins

I found no plugin for Phabricator, but there is a plugin for Jira that is like to be similar in high level functionality (creating tasks, commenting, etc.): https://github.com/Netflix/dispatch/tree/master/src/dispatch/plugins/dispatch_jira The amount of code doesn't look intimidating.

Phabricator already has a Python 3 client: https://github.com/disqus/python-phabricator which is in use at Wikimedia installation, for example, to automate RAID failures: https://phabricator.wikimedia.org/source/operations-puppet/browse/production/modules/icinga/files/raid_handler.py

All points that joining the puzzle pieces shouldn't be too hard- but we (I?) don't have much experience with dispatch development, so we should also, at the same time, try to document how a plugin is created and how dispatch works internally.