Feature-wise everything you need is pretty much there. Jasonette is not something I built out of nowhere one day, but I actually extracted it out of a fully functional complex app.
This is different from most approaches where some guy one day thinks 'hey wouldn't it be cool if there was a way to do this and this?' and builds it, because these approaches end up building out useless features that people don't even need or have bad designs because they built the whole thing based on their imagination.
I came from the opposite direction where I already had an app with tons of users http://www.textethan.com/ but was very dissatisfied with how tedious and time consuming it was to iterate on the app. I gradually started switching out each part of the app one by one so it can be remote controlled by JSON. And ended up with Jasonette.
If I can build a complex app, you can too.
Of course I wouldn't say it's 100% complete, but it's good enough to build any app you want.
In terms of roadmap, the next couple of months will NOT be focused on features, but instead focused on building out and releasing tools around Jasonette so it's much more accessible (and when i say accessible i mean something as easy as copy and paste to build an app in minutes while being as flexible as you want), as well as releasing a way to extend Jasonette easily (so if you want some feature but it's missing from the core, it's super easy to write one or have someone write one for you).
Hope this answers your question!