Not only does microservices and Kubernetes all over the place kind of diminishes whatever gains Linux could offer as monolithic kernels, the current trend of cloud based programing language runtimes being OS agnostic in serverless (hate the naming) deployment, also makes irrelevant what is between the type-2 hypervisor and language runtimes.
So while Linux based distributions might have taken over the server room as UNIX replacements, it only matters for those still doing full VM deployments in the style of AWS EC2 instances.
Also one of the few times I agree with Rob Pike,
> We really are using a 1970s era operating system well past its sell-by date. We get a lot done, and we have fun, but let's face it, the fundamental design of Unix is older than many of the readers of Slashdot, while lots of different, great ideas about computing and networks have been developed in the last 30 years. Using Unix is the computing equivalent of listening only to music by David Cassidy.
> At the risk of contradicting my last answer a little, let me ask you back: Does the kernel matter any more? I don't think it does. They're all the same at some level. I don't care nearly as much as I used to about the what the kernel does; it's so easy to emulate your way back to a familiar state.
-- 2004 interview on Slashdot, https://m.slashdot.org/story/50858