Agreed, a focus on maintainability is important. But which is more maintainable? Merging existing, working, widely deployed code - or forcing developers like Google to stay out-of-tree for five years?
My point is that the fact that some code is already being used on millions of devices and works *now* should carry some weight, even in assessing future maintainability. (It's much more likely that little-used features will suffer code rot, no matter what their conceptual purity.) At the moment it appears to get no weight at all.