I'm pretty sure that they'd ultimately accept kernel patches for the actual end-to-end functionality that Android needs, but there would be a lot of debate and

I'm pretty sure that they'd ultimately accept kernel patches for the actual end-to-end functionality that Android needs, but there would be a lot of debate and probably considerable engineering changes to kernel interfaces needed first. In practice, Android development seems to be more focused on shipping rather than on code quality, accruing technical debt in the process. To be fair to them, it's a project that is really an entire Linux distribution, requires lots of components written from scratch and not used anywhere else, and they're under massive pressure to keep up with the competition.