There is no such thing as a datacenter OS.
Simplification: An OS is a kernel and it's associated base software.
The kernel drives the hardware. You need to talk to disks. Memory. what not. Kernel is needed. You need to talk to the kernel and tie these components together. You write software. Boom, you have an OS.
A datacenter isnt a disk and memory and devices. its a bunch of computers which themselves drive these devices.
If you invented a "datacenter" with a bunch of disks and an API to drive them, then a bunch of CPUs and an API to drive them, and so on, you'll end up with a supercomputer and a single, unreliable, unsafe OS (which is exactly why nobody makes super computers anymore. They make clutsters of computers. Cheaper, more reliable. Clusters. Ie... datacenters).
The only thing that could be needed is a universal API for resource access. Need a db? Here's an API. Need disk space? Here's an API. and so on.
This is exactly what AWS is and does. S3 doesnt expose the OS. Its just a filesystem API. ELBs arent an OS. They're a load balancer API.
It turns out that below that, there's an actual traditional OS because thats the way it works reliably.
You have other ways to interconnect these systems in smarter ways (see plan9) but its always running a "regular" OS in the end, too.