Juju is a great project and you guys are way ahead of the game but the AGPL licensing is problematic for proprietary services built on that platform.
I could be completely wrong, mind you.
Using the database doesn't impose any restrictions on your software.
Even hacking on juju to add API'S you for your client software doesn't impose restrictions on the client -- it just means you are subject to the AGPL licence source distribution rules on the patched version of Juju.
I do not believe that _running_ your software on top of AGPL-licensed Juju makes one iota of difference.
The App Store is different: the restrictions the App store adds are at odds with GPL's defined freedoms. Not the same issue here.