Correct. Nothing quite like blowing Blood of the Dragon right as the boss decides to jump and you lose it and are locked out of your rotation for 45sec assuming you don't get a refresh in time (which requires about 10-11 seconds of leadup to refresh, not 1 skill).
I don't have a BLM up to anything worth talking about, but honestly I like the idea of B4 being insta-cast. Means that the "maintain the rotation" skill is very responsive, and gives time to throw up some oGCDs/handle a proc during the GCD (since I assume this would work like Bio/Combust/Aero/whatever with the delay coming afterwards). Think it'd be less prone to unintended consequences than changing the duration of AF/UI might have.