This is a follow up of my existing question Does GPL apply to proprietary software that is linked in through a compatibility layer, but has a new major focus (i.e. the shadow Linux).
Suppose a Linux-like kernel (i.e. "shadow Linux") is developed from scratch, which use a very similar kernel data structure and intra-kernel APIs as Linux kernel. But this new kernel is released under permissive open source licenses.
Then driver (or kernel modules) developed for shadow Linux don't need to release their sources. But considering the similarity of the kernel of Linux and shadow Linux, it is very straightforward to develop a compatibility layer in the Linux kernel that can let Linux to use proprietary driver binaries for shadow Linux directly.
Now if you want to develop a driver for Linux without releasing your code, you just need to develop a driver for the shadow Linux.
Is this possible (not considering the difficulties of the development of the shadow Linux)?
(1) The shadow Linux can't replace Linux which take too much effort to develop. To simplify the development of the shadow Linux, it doesn't include anything that is not needed to develop a kernel module/driver, and it contains a lot of bugs and performance issues and is not a production level kernel.
(2) To prevent any copyright issues about Linux, althought the shadow Linux kernel's data and API structure is very similar to Linux, they are not the same, e.g. not the same name and even structurally redesigned but still allow a compatibility layer to be developed with ease.