And the middlebox brokenness is due to a lack of versioning. Virtually all middlebox brokenness is a result of a lack of versioning and poor upgrade paths - usually from people demanding backwards compatibility above all else.
I view it as more of a consequence of "fail closed" thinking than a lack of versioning. As we've seen recently with TLS [1], even protocols with explicit versioning suffer from middlebox brittleness.
