Android OEMs are not in the business of writing kernels, though, and the changes they do are minimal. And their HAL/chipset code -- the thing they might actually care about as IP -- is not governed by the GPL at all, nor is any of the enormous volume of system and userspace code they write.
It's a neat initiative and might yield something interesting, but if the Linux kernel was replaced by Fuscia the ramifications are seemingly very minor. Android's many issues have never been at the kernel level.
Qualcomm has no obligation to GPL their kernel drivers. Nor does nvidia, or any other KLM maker. This has never demanded that kernel drivers be open sourced. That's why it's impossible to make a runnable AOSP image for many devices.
Vendors still make generally minor changes to the kernel, but these are not unique or special or some competitive edge. They've just nuisance necessities.
It's way more grey than that. Nvidia claims that their driver doesn't need to be opened because since it's A) from a codebase that existed prior to the Linux port, and B) doesn't actually import any Linux code or symbols (that's left to a dual licensed shim layer), that in a legal sense their driver isn't 'derived from' the Linux kernel and isn't subject to the viral parts of the GPL. And, all of this is the greyest of grey area. Towards that end, Nvidia has been committing to Nouveau lately for Tegra chips because I think they realize how precarious their legal situation is for chips essientially designed to run Linux.
That reasoning doesn't apply to most kernel drivers, and those vendors are just openly in conflict with the GPL.
Literally any driver that has a piece that runs in interrupt context has to have (in part) a kernel mode driver under Linux.
On top of that, GPUs generally have to have a kernel component, even under systems that put as much as possible under user mode like sel4, because they have their own MMUs that can subvert kernel integrity.
It's a neat initiative and might yield something interesting, but if the Linux kernel was replaced by Fuscia the ramifications are seemingly very minor. Android's many issues have never been at the kernel level.