The memory that XNU and Darwin are technically open-source projects is a curse that brings one only suffering.

I feel like Apple wouldn't want to make full Linux work on their hardware, but they could enable their Darwin kernel to emulate Linux syscalls and provide a way to boot into a mode that basically loads the kernel and whatever Linux shell you want

This path is already taken and it didn't sell Apple hardware in masses.

https://en.wikipedia.org/wiki/MkLinux