To contribute to this, some months ago we moved from a LiquidPlanner instance with a few thousand tasks to PH. From what I remember now, if conduit was a bit more powerful it would be a lot easier to do such things (it's almost like if PH don't want people to migrate from other systems into PH). The basic things missing from conduit, last time I looked at it, was the ability to specify dates other than the current one for any action you do (e.g. task creation date, comment date).

Building on the work from the Blender team (thanks!) we have been able to plan a migration of ~40,000 trac/trello tickets into phabricator. Summary: (A) a lot of work (B) gross code (C) basically working (huzzah!). If you are considering doing something similar some examples from what we did might help. I'd only go down that path if you have significant expertise in the source system and phabricator (as in if you break your phabricator install you will need to fix it on your own).

Closed by commit rP7d9eb8baaf86.