> AFAIK, vanilla kernel improved a lot in terms of functionality, so Android can work on vanilla kernel if code will be adapted to use these new APIs instead of Android homegrown APIs. Anyway, it's open source, so anybody can use Android patches without restriction. I see no problem here. Kernel version 4.4 is fresh enough for me: https://android.googlesource.com/kernel/common/+/android-4.4.... .

What I'm trying to tell is it being possible doesn't mean it is practically possible.

Android specific API or subsystems are one part of it, then there is device specific patches. Kernel and patches being open source makes it possible to switch to a new kernel version but I've almost never seen that exercised. Few years ago the stats were that a typical consumer phone contains millions of line of patches on top of the selected upstream kernel version. It is not feasible to rebase a typical device to use a newer kernel version, and it really shows: I've seen only few phones that got a newer kernel version than it originally shipped with, switching from an ancient kernel version to only slightly newer but ancient kernel version.

> BTW. I'm not sure if my distro (Fedora) will work with vanilla kernel without Redhat patches. There was times when it wasn't. I compiled kernel myself with my own patches and configuration in between 2001-2008.

I'm pretty sure it'll. Linus himself uses Fedora and he likes his kernel pure vanilla :)