We have many users which commonly file tasks via email from their phones while in the field. It would be much more convenient for them to be able to email "firstname.lastname@example.org" and have that email address use a specific edit form for maniphest tasks, rather than retyping the same set of subscribers and projects etc every time.
I think you should already be able to add subscribers and projects (and take some other actions) with Herald, by writing a "Global" rule using the "Receiving email address" condition. Here's an example:
Does this cover things? Could we add new actions to fill in any gaps?
Depending on what's missing here, I might want to wait for Nuance before moving forward on this. Specifically, I think this capability is potentially reasonable (and we might have built this, instead of the "Spaces" binding, if EditEngine had been written first), but want to make sure there are use cases which it's a significantly better fit for than either Herald rules or Nuance queues so we don't end up with a system that is completely eclipsed by two similar, more powerful systems.