The biggest mental leap for me is that you are using JSON objects to define sequential code. JSON defines an object as unordered. Obviously your compiler maintains order properly, however it just "feels wrong".
Like I said there is no way you can convince me to write code in a browser (unless there is an absolutely magical benefit), so writing fjson manually looks difficult both in the amount of extra syntax, as well as trying to connect the data to what it's doing.
The last thing that would hold me back is the debugging experience. Will i get back which lines im my documents are causing runtime errors, is there any static checking in place to make sure the strings of code are syntactically correct?
It's a big leap for me, but that being said, I definitely applaud you for developing something new and experimenting. I'm interested in seeing where this evolves.