Hypothetically, an Android vendor could build a notification service separate from Play Services and deploy it on their Android builds. Has to be a vendor (or, more broadly: "someone who controls the OS down to the kernel level") because the notification technology involves some heavy abstraction-breaking footsie between the physical link layer and the TCP stack.

But the two big challenges there are:

- odds are the first several iterations of it will suck, so they'll be competing with an already-working solution that most users have no concerns using (significant market uphill fight, with the only major value-add being "We're not Google").

- we've just traded one master for another. Ultimately, unless someone builds an open-standard at the Android distro level that includes an API to allow users to establish a notification source, the distro owner still owns the notification system (and there's no reason a priori to assume they're less evil than Google). And designing that API to be abuse-proof would be a challenge; do it wrong, and we're back to the bad old days of sub-one-day battery life on an idle phone.

It'd be a hell of a cool project for someone to take on though.