I’m currently investigating Putting Web Apps on SAFENetwork by Adapting Existing Frameworks which may start to give you some options before long. I’m still researching, but more hands looking into this and evaluating would be great.
I think there will be several options, so I envisage setting these out and then choosing one to have a go with. My guess at the moment is a JavaScript framework that offers different levels of API for different app capability. Example (only!):
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CRUD: simple storage i/f (RESTful access to JSON objects/documents). Not very useful, but easy to provide, and enough for simple apps.
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CouchApp: Cut down CouchDB API, with a subset of DB functions implemented on the client in JavaScript. Limited scalability, limited features, but easier to port existing apps expecting a NoSQL style DB, and especially some simple CouchApps, of which some are quite interesting.
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PouchDB: As 2, but with full NoSQL CouchDB style API for offline operation (auto sync with SAFE storage when connected).
The above its to illustrate my approach, NOT at this stage a plan! 
Anyone who can add to my knowledge or wants to go investigate and try out ideas like this, let’s talk (please post on the topic I linked at the start of this post).