A. Zonenberg's "antikernel" project was an interesting take on eliminating the entire notion of a kernel from an operating system. It is like an extreme version of an exokernel with the kernel spread around everywhere up to and including peripheral devices.

When thinking "beyond Linux" perhaps we should also be considering the possibility of "beyond OSes as we know them" instead of swapping in one Unix-alike for another.

Linux is not a secure operating system.