Android Treble is, at long last, decoupling Android OS porting from the cycle of BSP support. It's only for Android 8+, so the impact won't be widespread until later this year and into 2019. But this should enable vendors to lengthen their update support more independently of the underlying kernel and driver support.

https://source.android.com/devices/architecture/treble

Large parts of Android-the-OS is implemented in middleware running on the same runtime as Android's apps, which should have made this kind of portability possible earlier in the development of Android. But here it is.