And if it isn't non-blocking? What if I'm writing a game and want to run parts of the rendering, AI, physics, etc. in parallel? Do I create a bunch of containers for each subsystem of my game and have them all communicate via IPC? This doesn't sound like a recipe for good memory/performance characteristics.

But we’re talking about javascript here, a language that is async about almost everything.

I completely agree with what you’re saying for those other problems you describe. But for the typical node.js webapp, doing the one-container-per-core is perfectly fine.