For those that haven't been paying attention, since last year there's been a concerted effort to mainline more of Google's Android changes into the mainline Linux kernel. Android patches that went into the mainline Linux kernel previous suffered some rot, but this latest effort has the backing of several companies and is finally coming to fruition within stable kernel releases.
Lots of the Android work landed into the Linux 3.3 kernel staging area and with the Linux 3.4 kernel there are more Android patches.
Kroah-Hartman was asked at the 2012 Linux Foundation Collaboration Summit in San Francisco about Android as a first class citizen to the Linux kernel. Greg's response was basically, "It is today...Linux 3.3 kernel can boot Android user-space...while eating the battery alive."
The latest Linux kernel can boot Google's mobile platform, but there's still more mainline work to be done and it's at a greater rate of power consumption than Google's modified kernel. Greg went on to add that it's just not "up to us [the mainline Linux kernel developers]" but Google also needs to make some changes on the Android user-space side for interfacing with the vanilla kernel. This will likely take some time on Google's six-month release cadence for Android to make the API changes.