i don't really believe that the phantom pain isn't in active development. even the earliest screens of mgsv (before we even knew it was mgsv) were of segments that would appear in the phantom pain. i'm willing to go out on a limb and say a lot of the time is being spent on asset creation, balancing, and implementation.
i know kojima gets a tremendous amount of shit for saying the phantom pain is "200 times bigger" or whatever, but i do believe that the game has considerable scope that is hard to balance against budget and time constraints as well as the shackles of old hardware, not to mention that this kind of open plan game design is new ground for kojima productions, and possibly the stealth-action genre as a whole.
i do agree that it probably won't release until after e3 2015.
if it isn't realising before e3 2015, it'd probably be wise to not have a showing at e3 2014 to avoid blowing the load too early either. mgsv really needs a submergence period after ground zeroes releases.