I have been following the JBI spec closely for a while - and something that Eric Newcomer said recently summarized very succintly the difference between architecting for the vendors vs architecting for the customer.

"JBI is entirely focused on an API for integration vendors. Application developers are unlikely to ever use it".

You look at something like BizTalk Server, or even better, at Indigo, and its quite the opposite.

Customers want software to be architected to solve their challenges. Not software specs that are focussed on keeping the JBI-compliant integration vendor ecosystem on life support.