the distributed computing model is pretty nice in theory (maybe not in practice) and the uniform system APIs are also nice. The userspace tools in particular are just plain better (structured regex commands are quite a bit better than ed-style and I find myself using them far more frequently in vis than I do in vim, they're far more composable and intuitive).

The biggest thing is the heavy reliance on union file systems (and file systems in general) and an extremely simple syscall API. It's a heterogeneous-networked-node OS so it handles realistic workloads natively with primitives designed for it instead of piling complexity on top of Unix-like APIs (ie. Linux). I dunno, I just think a lot of the modern "cloud native" stack is unnecessary if you had an OS actually built for the workloads we have.

It could be used to replace k8s-based deployments (also Docker Swarms, etc.) since system interfaces on Plan 9 are namespaced and containerized "out-of-the-box" as part of its basic design (and this is one of the most prominent additions compared to *NIX). It's not a hacked-on feature as with Linux.