I'm curious about the limitations that prevent these apps from writing / caching local data. It doesn't seem like the paradigm would have to change entirely to support that.
There aren't any, with hyperview you actually own the hypermedia client as well as the server and you can write and cache local data in the form of custom extensions you make to it.
So, basically it's like every other non-native development environment for mobile: basically useless when you want to use any feature of the phone.
These things always implement the easiest bit of mobile development (the UI) and then make everything else harder, so it's useless for anything non-trivial.
I think that needs better documentation though.