The idea of a multi-user time-sharing virtual memory operating system is seriously outdated.
Today, the server OS could be based on a one user, multi computer abstraction, with multiple gigs of memory, solid state storage, and reliable gigE+ network as assumed essentials.
Entire sub-systems of the current linux kernel can be omitted.
Most of the VFS layer, with so many optimizations for spinning rust. Right out.
Paging, swapping, shared objects, address randomization and PIC. Right out.
User access controls, file access controls, network access controls / firewalls. Right out.
Of the 50,000 device drivers in the linux kernel, probably 50 deserve to be supported.
For a workstation with graphics / GPU and console support, and every pluggable external device support, maybe some sort of legacy emulation layer would work. Basically run a linux VM for backwards compatibility with those 50,000 devices. Would be less work than implementing those drivers...
Remember, Linus was once a 19 year old with a dream, and a small repo of prototype kernel demo code, 25 years ago.