The objection appears to be "JSON isn't necessary, as it's just a simple linked list. Users could write their own". However, I would think this is a useful feature.
There are applications I could think of whereby a JSON would be necessary, or at least very convenient.
(1) Is there a standard way to convert GFA into JSON? Or do users write their own scripts?
(2) Is there a conceptual reason why GFA doesn't convert into JSON?