The battery life question is all about compromises. It is interesting what Apple has in mind for the rMBP. For the Air it is obvious: no redesign, no high resolution screen, but awesome battery life. The bigger battery and the ULV Haswell processors made that easy. But for the 15'' rMBP it is harder to predict the answer to this question, because there a lot of technical limits like power hungry quads and retina screens and their thinness paradigm. And on top of that, the last years compromises were more about performance. All these needs contradict each other, so Apple offers a compromise of what they think is a optimal solution. Some people here have way to high expectations concerning the battery factor.
I am not a fan of loosing performance for battery life, because i have nearly everywhere a power supply. I can hardly imagine an usage scenario, where you do heavy stuff on the go. Last years rMBP battery can be emptied in an hour under heavy load. Even with Haswell (and Iris 5200) the problem would be the same. For light usage I predict an 1-2 hour increase based on the technical limits. And if you do just light task and you are not fine with the up to 7 hours, you won't be satisfied with up to 8-9 hours. Why don't you buy an Air or an iPad? Some people basically want a 15'' Air with an IGZO retina screen and a ULV quad. Ok, but this would be a different product.
And if Apple would really care about battery life, they would rethink the thinness paradigm of their products in a time, where battery technology is stagnating. I mean who really sat in front of a 15'' cMBP and thought that this thing is way to big and heavy. Or who held an iPhone 4 in hand and thought please make it thinner i can't lift this thing up anymore. Not making things thinner for the sake of thinness would be the easiest way to provide good battery life and the space for high performance components. These incremental thinness improvements are overrated. With more space Apple could easily keep a more powerful dGPU, provide better battery life and add all the stuff like ethernet, multiple USB-ports and a Kensington locks.