Obviously you can add modules calling to C/C++ functionality to a scripting language runtime easily (and the interface to do that is already available for the browser implementation).

In the above link Node could be described as a Chrome V8 distribution with modules enabling building a web server.

Adding threading to a non-threaded scripting runtime is another ball game.

The point is that Node was forced into this model by V8 limitations, then sold it as an advantage, however, it is only one way to solve the problem with its own trade-offs and you have to look at the specific use case you are looking at to see if it is really the best solution for your use case.