Threading at the JS level in node is really ineffective. V8 has a global lock on all JS objects that prevent them from being passed between threads. The only way to allow threading is to serialize and deserialize the objects into new "isolates" (V8 language). V8 does this for some pretty obvious reasons, you wouldn't really want to allow threading at the JS level in a browser, now would you.
You can use threads if you dive down into C++ land, but event then, you should have a really good reason for doing so, because if you're only manipulating objects for processing you're going to have to serialize into a C++ data-structure, process, and then serialize into a JS object. Threads in node are good for doing process intensive work that doesn't require any two way input from the main event loop, otherwise it's very unlikely to be worth your time or effort.
This is why fibers are kind of silly for node and is also why process intensive programs should most likely be avoided in node (with rare exception). Please use node for what it is good at; it's a short lived connection proxy maven, and good at ancillary front-end work that requires complex state transitions (i.e. mobile). Working it into a monolithic stack is just asking for trouble and pain. No serious architect should consider it for a large monolithic rendering stack.