I took an OS class but wonder nonetheless: If you aim for 0 compatibility, perhaps even can design your cpu, could an OS be much simpler? Could some standard components (paging etc.) be avoided altogether? Or is what we have a minimal set already?
The microkernel idea is to move everything that can be moved, out to user-space. The minimal OS services is typically thread management, address space management, and some kind of IPC. And if you choose not to provide virtual memory or memory protection, you have a very tiny core OS.
Everything else, all the "normal" OS services can be provided by application level programs - device handlers, file systems, network stacks, time services, graphics,... almost everything.
Yes, but a lot (possibly most) of the benefit is likely to be from dropping bug-for-bug compatibility with defects of preexisting operating systems and instruction set architectures individually. (Like x86 segmentation or unix tcsetattr/termios, for a pair of very obvious examples.)
For paging specifically, you'll have something functionally equivalent unless your system is deficient in the same ways a 6502 is (no virtual memory or memory protection). You might come up with something functionally equivalent but better, but if so that would be a novel discovery (either in the scientific sense, or in the sense of "I discovered a research paper from 1960 that solves this problem trivially as long as you have larger than 6-bit bytes and more than 64K[0] of RAM.").
0: Something like four rooms of vacuum tubes in 1960 money, which is why it never caught on. (/not-even-all-that-s)
* the illusion of multi-tasking! (context switching) (when you have one CPU-core)
* the bridge to your hardware! (e.g. ignoring the basics like your CPU/RAM/motherboard/IO devices, network interfaces themselves are an endless, unreliable torrent of data!)
* security! (unless you are literally God and make everything yourself, you have to trust ~something~ external)
* and more....
and complexity for CPUs (even ignoring legacy cruft) comes from :
* Branch prediction
* Register renaming
* Optimizing dat IPC
* More hacks for performance!
* Performance!!!
* and more....
Because at the end of the day, no matter how "simple" things are, creating the universe from scratch is never simple