Maniphest tasks can be modified by Herald rules based on their project or their space, Herald can also add projects but cannot add (or remove) spaces.

Our situation: Phabricator is used in our context to order the work of different working groups and not all of them should see every other object. A Herald rule that could assign a certain space based on a project would solve this issue.

Why?

• Spaces are (as far as I can see it) the easiest way to modify object's visibility. If Herald rules can modify spaces, this would be a simple possibility to facilitate that no object with undesired policies get's created.
• Spaces could also be applied manually when creating or modifying a new object. However, most people tend to forget to set the space for new tasks quite shortly. An automatized solution would solve this issue.
• We do not only work with different groups but also with several co-operation partners who we want to give access to Phabricator. They should only have access to the projects they belong to but should not see anything else. Since it is only possible to recognize what you can see but not what other people can see, mistakes in handling policies could remain undiscovered. Therefore, I would prefer some way of automated way of handling policies.
• I understand the problem with policies described in the project user guide, and I see why the best way to handle this is that the object's policies are not affected by the associated project. However, by extensions of the Herald rules for Maniphest task, I could make sure that the policy is automatically set the way I intended it (for instance, changing the viewing/editing policy to a specific space when one or several projects are tagged with a specific task).

Great work with Phabricator, by the way. :-)