It's not uncommon for Apple to have private branches that are merged back to their OSS projects after features/changes/devices have been announced -- it's been occurring a few times in LLVM and Clang-land. Taking a quick glance over the git history seems to point to commits referencing 3.0 though?
As long as Swift continues to have strong reliance on Apple, Swift on server-side will run the risk of being a second-class citizen. It's unlikely to have a well-established ecosystem of external developers either because Swift currently attracts primarily iOS developers. So, till Apple makes some moves to show that it considers server-side a first-class citizen, or you see a very obvious external developer ecosystem building for server-side Swift, I'd recommend not using it there.
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[ 3.8 ms ] story [ 36.8 ms ] thread[1] https://github.com/apple/swift/releases
Edit: added GitHub link.
https://github.com/apple/swift-evolution#implemented-proposa...
[1] https://github.com/apple/swift/releases/tag/swift-3.0-PREVIE...
[1] https://swift.org/blog/swift-3-0-preview-1-released/