Linux kernel is the most sucessful free beer UNIX clone, but it is by no means the only one, and if the trends on IoT and cloud infrastructure are any measure, in a couple of decades we might still live under POSIX monoculture to some extent, but Linux most likely won't be the kernel underneath.
https://github.com/abseil/abseil-cpp/blob/master/absl/base/i...
They also have for years had major patches to TCP which Linux refuses to adopt. Some details at:
https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-tc...
These won't make binaries "not run" as such but they are necessary for the correct and efficient operation of large-scale distributed systems.
QUIC, Snap/Pony, and user-space thread scheduling are strictly superior to what happens inside the kernel and their development makes the delta between prodkernel and upstream kernel less relevant over time. They also, collectively, make Linux itself less relevant.