Very arbitrary, but:
My best guess would be it’s maybe a hundred to a thousand people worldwide. Most of those will be developers who (arguably) would be ok with editing json as well. The main audience should be clinical modellers, but most (>90-99% of those) will only edit using a GUI.
So yes, it will mostly be small changes. But already the jump from GUI to editing ADL by hand is huge. I think the jump to JSON will be too discouraging for people like me. FWIW I edited quite a few (>10) yaml files, but never json, it feels just too hostile/ machine like.