I agree. Harnesses are quickly becoming the next systems programming frontier. The OS analogy is apt and often made--just like browsers have been compared to becoming "platforms" and "OSes". Another analogy that is obvious is threads/processes and agents and sub-agents: all the concurrency, shared resource access, cooperative multitasking, etc problems are emerging again.

It will take some time to shake out, but lots of old ideas are new again. Personally, I'm mining lisp machines, homoiconicity, actor models, and other ideas for my harness designs.