I think you're reaching towards the concept of a Single System Image [1] system. Such a system is a cluster of many computers, but you can interact with it as if it was a single computer.
But mainstream servers manage hundreds of processor cores these days. The Epyc 9965 has 192 cores, and you can put it in an off the shelf dual socket board for 384 cores total (and two SMT threads per core if you want to count that way). Thousands of core would need exotic hardware, even a quad socket Epyc wouldn't quite get you there and afaik, nobody makes those, an 8 socket Epyc would be madness.
you can build these without shared memory using standard distributed database techniques for serializability and fault tolerance. i dont think its a particularly good idea. there's nothing great about running 'ps' and getting half a million entries. using the unix user/group model isn't great for managing resources. its not even that great to log in to start jobs. the only thing your gaining is familiarity.
building better abstractions - kuberenetes is an example, although i certainly hope we dont keep being stuck there - is probably a better use of time
But mainstream servers manage hundreds of processor cores these days. The Epyc 9965 has 192 cores, and you can put it in an off the shelf dual socket board for 384 cores total (and two SMT threads per core if you want to count that way). Thousands of core would need exotic hardware, even a quad socket Epyc wouldn't quite get you there and afaik, nobody makes those, an 8 socket Epyc would be madness.
[1] https://en.m.wikipedia.org/wiki/Single_system_image