The AEBS upgrade to Time Capsule looks potentially more than the surface of just adding a shared drive to me. Presumably it would 'fix' the software issues with shared drives via AEBS (for Time Machine or otherwise) - including a presentation of USB connected drives as a shared device (according to one poster from MacWorld).
I wonder if 2 AEBS's connected via Ethernet would present both drives through the same gateway (without requiring 2 wireless attachments by the client). If so, would this be an alternative to a NAS system? (without the RAID stuff of course). All the specs (and Jobs presentation) refer to the internal drives being server grade... Potentially another advantage if this really translates into bus connection and quality....