_ph_ meant to write "This way, they can at least upstream everything which doesn't fall under these restrictions." (note the deleted comma before "which"), i.e., they can at least upstream something instead of nothing.

As mentioned I don't care, after university my main UNIX platforms were HP-UX, Aix and Solaris with their respective system compilers anyway.

Linux is already getting replacement candidates in IoT space via Zephyr, NuttX, mbed, RTOS, Azure RTOS, and who knows if Fuchsia will eventually get out of the lab, so be it.

No, for practical purposes, there is not. You can only enforce delivery of the source when a product based on GPL software gets delivered. But of course companies, which create software, know about this. Any usage of GPL software for delivered products only happens after the decision to publish the created software has been made. In doubt, companies tend to not use GPL software as part of deliveries.

GPL advocates try to claim otherwise of course.

I keep wondering if Microsoft opens up the Windows Kernel ( And Kernel only ), would it change the landscape much.

On Android Linux is an implementation detail, most of it isn't exposed to userspace, not even on the NDK as Linux APIs aren't part of the stable interface specification.

And ART is being ported to run on top of Fuchsia as well (https://android-review.googlesource.com/q/fuchsia), so...