All that does is simply mention that they improved battery life slightly with better background management. That was years ago. What you are talking about is an overarching change that encompasses every device it runs on. Optimization, like the Moto X for example, is specific to certain hardware the software is run on. Sure, either one would be great. But let's remember we are talking about optimization for specific hardware.
Look at when ICS came out with the Gnex. Horrible battery life, no optimizations to make it better. 4.1 rolled out, still no optimizations for the specific hardware in the Gnex. Then the Nexus 4 with 4.2. No optimizations. Same with 4.3. But with the Moto X and 4.2, it gets MUCH better battery life than the Nexus 4. Why? Because Motorola paid special attention to the hardware that the software would run on. Having this special attention to the hardware allowed them to optimize the OS to make better use of the available resources. Even the Optimus G did that with LGs skin more than Google did with the Nexus 4. If history has shown us anything, which I think it has, then it showed us that Google wants to build a base OS. A base that other manufacturers can build on. However, because they are making a base, it makes it difficult for their base to be optimized for specific hardware when other manufacturers won't run their version on that hardware.
That is another reason Apple gets good battery life on their iOS devices. They don't have to worry about making a base OS for others to build on. They do all the optimizations for their hardware themselves. Essentially, Apple makes the base OS and optimizes it themselves for their hardware. This is split up with Android. Google makes the base and slaps it on a Nexus device. They send out the base OS to other manufacturers and they do the optimizations for their own devices (think HTC One, Moto X, Optimus G). So there is a big disconnect between the Nexus smartphone and where optimizations truly occur.
History has shown us that there likely won't be any major battery optimizations in stock Android for Nexus smartphones. I don't know how else to say the same thing to you. It seems like whenever I say something, you just want to argue with me for the sake of arguing. Maybe you don't like that I am skeptical of the Nexus 5s battery life. I don't know. But I am not the only one here who is skeptical of a measly 2300 mAh battery powering a 5" 1080p phone with a Snapdragon 800. You seem to think battery life will be fantastic. And that's great, think whatever you want. But I think it's important to manager our expectations and draw from Google's history and other devices to get an idea as to what we can expect. And I can honestly say I do not think we can expect anything mind blowing.