Exporting data from Phabricator on an object level (task, project, user, etc.) can be quite difficult. Importing data into Phabricator is also not as easy as it should be. See T715 among others.
The schema design of Phabricator relies extensively on relational ids and there appears to be no easy way to export individual data sets as "open data" with object metadata descriptors. These seems to me to be a potential problem for integration with and possible future migration to other tools.
The premise that Phabricator will be the "be all, end all" software development tool is as yet unproven. In fact, it is probable that in the near future something new (and perhaps better) will appear. It behooves us to seriously consider how to get data out of Phabricator if the need arises.
I propose that the evaluation ask the following questions:
Question 1: Is it possible to readily export Phabricator data to another platform?
Question 2: Is the Phabricator API able to provide and facilitate open integration with other platforms?
Question 3: How does Phabricator measure up against other Software Development tools in regard to "open data" export and import?