Loading JavaScript (of which JSON is a subset, of course) has been explicitly permitted for a long time now, as long as it's downloaded and interpreted by the built-in WebKit engine.
Phonegap/Cordova has a developer app that works similarly, allowing you to hot-load code updates without forcing you to reinstall the entire app.
You're right, to be clear, in case of Jason it's not even "downloading code" because all the native code is already there on the app itself. Instead what gets downloaded is a flat JSON text, which then gets interpreted into calling the APIs available on Jason.
Thanks for bringing up Phonegap/Cordova so I can describe the difference. In case of Jason it directly accesses native elements like UIStackView, UITableView, UILabel, UIImage, etc. because I manually built everything from parser to renderer to do exactly that. You are basically remote controlling these native elements and calling native functions by scripting with JSON instead of writing objective-c code.
I feel like a lot of people on this thread thinks it's based on webkit, which is understandable since a lot of people claim to be native when they're just a native wrapper for HTML5. I think I need to clarify this point in future pitch.
Yes, that would be worth some clarification. I made that assumption myself. It's my fault for not having read carefully, of course, but if I did it, others probably will too. :-)
Phonegap/Cordova has a developer app that works similarly, allowing you to hot-load code updates without forcing you to reinstall the entire app.