This is really interesting and welcome contribution in an important space. Three features that would make it compelling:

1. Offline. Making the local datastore as "invisible" as the memory cache and the cloud - keeping everything in sync under the hood. 2. Push. Notifying clients when changes occur. 3. Diff. Efficiently handling changes in larger values.

I realise none of these are central to the challenge they faced, and congratulate them on an elegant solution for their situation.