I just made the (implied) observation that anyone deploying nginx shouldn't even bother enabling spdy in 1.4 (stable) because effectively nothing will use it anymore. It was something that people who use "stable" software were able to benefit from starting in May 2013, but it is now no longer and won't be again until nginx reaches 1.6. That is, unless spdy/3 is dropped in favor of spdy/4 by then.
(edit: fixed date)