It was too dogmatic. Lowest common denominator meant APIs had to shove square pegs through round holes. Unix had already partially gone down that path and stopped. IMO with good reason.
Then again, perhaps in this era of ever expanding storage and compute, maybe someone can make it work even better?
There's nothing "dogmatic" about containerization and providing services through userspace (IPC that's modeled as interaction with custom filesystem trees) rather than bespoke syscalls whenever feasible, which are basically the foundations of the plan9 approach. We do strive to do both in modern systems, but the approach to the problem space is clumsily bolted over the original system interfaces, and becomes overly complicated rather than elegant.
Then again, perhaps in this era of ever expanding storage and compute, maybe someone can make it work even better?