I don't mean that they won't release it, but that they haven't indicated any intention to release it except as a binary thrown over the wall into their developer program. They just held a very big developer conference and made no mention of it being free or open-source. Their "LLVM work" up till this point has all been C and Objective-C stuff that's part of the LLVM Project and they have made a big point of that, so I don't really see how it reflects on this, which is not part of the LLVM Project and is not based on existing cross-platform languages where they're competing with other open-source tools.
A proprietary Swift even sort of makes logical sense. I could easily see Apple thinking that since Swift is intimately tied to its proprietary system frameworks, Swift should be proprietary too.
The C stuff wasn't part of LLVM until Apple made clang, a separate C frontend which uses LLVM. It's part of the LLVM project only because they contributed it; there's no particular inherent reason it had to be.
A proprietary Swift even sort of makes logical sense. I could easily see Apple thinking that since Swift is intimately tied to its proprietary system frameworks, Swift should be proprietary too.