Arlo, I understand the reasoning to eliminate the old server based sync system, and the associated storage and maintenance expense. The email sync method is OK, but could you add an option to "simply" sync the database between linked devices via wifi or bluetooth? There are occasions when I want to to make changes in my setlist database on the job. It is rather cumbersome to upload the database email to the other members that need the update, then they have to install the update from the email, keeping in mind that all devices would require early available internet connectivity to do this. If the devices are linked, however, the database information could be transmitted from the master device to the subordinate devices via the link. Of course, all devices would require linking capability, and be linked. Sound feasible?
(no charge for preliminary engineering)
Peer to peer networking options aren't great -- some options aren't cross-platform compatible, and transferring a database file of 1 MB or more could be unreliable. Anyway, I'll put this on my wish list.
Meanwhile, if you're using all iOS devices, you could use the AirDrop function provided by iOS. For Android devices, you could use a Wi-Fi Direct app like Send Anywhere (https://play.google.com/store/apps/details?id=com.estmob.android.sendanywhere).
AirDrop does not work on iPad 2-3, and that's what we all use. Perhaps there is an app that provides file transfers between devices. I'll let you know if I find a solution.