Download all documents of the pool
Yes, I can imagine a that submitting a form redirect to a service task which hold a connector to build an archive based on the different document. This would return a URL string that could be used in the next form so that someone could download it easily, from a HTML widget or eventually from another file widget (as download link only).
I believe this could be done on subscription pack with a contingency, so that once on click on a button, a fied (maybe a HTML one) is updated with the newly computed URL.
Note that depending on the size of whole pool documents, the archive creation can be long and ought to be seen as an asynchronous mecanism.