I'll admit that I don't know much about Node.js beyond the (very) basics, but if this (not having "the cost of a thread") is where Node.js shines, then this pro

I'll admit that I don't know much about Node.js beyond the (very) basics, but if this (not having "the cost of a thread") is where Node.js shines, then this project might be very good on top of the .NET CLR 4.0. There's been a lot done under the hood to support async / parallel processing (specifically, reworking and optimizing the built-in ThreadPool, which is used for very short tasks to avoid "the cost of a thread").