According to one Apple developer who works on the project it will _likely_ be open sourced, though the developer says they don't know if that's true or not:
Sure, sorry - I'm not sure which SA threads are free and which require payment. This is the relevant bit:
"Is this under NDA?
No.
Is this open source?
Not yet. It probably will be, but I can't make promises. Right now, our repository still has a lot of history that we don't want to make public, and we have a lot of work to do before we release."
Swift on the Server with some modern CSP flavored concurrency mechanisms would Rock! Then combine that with a Swift-like language that compiles to Javascript, and that language could take over the web.