https://source.android.com/docs/setup/contribute/licenses says most of the Android userspace is Apache 2 licensed. While they can’t close source the Android branch of the kernel, they could close-source new userspace code and it would probably diverge from the last open source release quite quickly.
Realistically, that would probably be sufficent to make Android functionally closed-source, even if the GPL bits were still available.
I think it would still be a good question to ponder, even though that isn’t what has happened yet.
What IF Google decided future versions were closed source? How would that not affect our open source alternatives?
Google can decide all they want, but they can’t close source Android due to the GPL.
https://source.android.com/docs/setup/contribute/licenses says most of the Android userspace is Apache 2 licensed. While they can’t close source the Android branch of the kernel, they could close-source new userspace code and it would probably diverge from the last open source release quite quickly.
Realistically, that would probably be sufficent to make Android functionally closed-source, even if the GPL bits were still available.