They want to control your network. They want to inject advertising into everything you do. They want you to have no choice but to use DNS servers they control.
That was just about my first thought too: "what are the odds this will have/allow something like Privoxy to do ad-filtering?" To be fair, I haven't bothered installing that on my own firewall just yet (relying on ABP and Ghostery for now), but it's on the to-do list - and having seen recent upturns in ad-blocking usage lately, I'm absolutely certain Google will have noticed that upturn too, and strongly suspect it's a factor in any move like this. (It's also interesting to note that Apple have just added support for ad-blocking in Safari without jailbreaking to iOS 9 - probably not something welcomed in Mountain View!)