You need some form of structure unless you want a zillion roundtrips. JSON is cool because it provides the basic structures (scalar, list, map) in a consistent and reliably parsable form. You don't need a context-aware 50 page ABNF to be able to parse it cleanly.
(don't even get me started on trying to write a proxy for IMAP that's aware of the connection state)
(don't even get me started on trying to write a proxy for IMAP that's aware of the connection state)