I suspect it's a hard issue for the App Store model.
You don't want a situation where someone updates App A, it updates a lib, then App B breaks because it hasn't been checked against the new library. I know you are a good developer who would check that, use major / minor library versions correctly etc. but there are lots of developers on the App Store. Or the fun case of updating App A, it updates a lib and then magical new features appear in App B that Apple doesn't like.
You'd probably have to use some sort of strict library versioning system where every app version is tied to a very specific library version. Are developers in general going to be disciplined enough to actually keep their apps all in sync on a specific version so older versions of the libraries can be removed? Or does this just mean every app from a developer will end up having its own slightly different revision of the lib tied to them? If it's the latter its probably not worth Apple's time adding all the complexity to manage the libraries to the App Store system.
And given that’s a new approach in a Unix-like environment, let’s call it Nix, and the content-addressed download location should probably be called the binary cache :)
[Not really, Nix integrates a build system into the process, and there was prior work I can’t remember that was binary-only and so closer, but the essence of the idea is very similar.]
You don't want a situation where someone updates App A, it updates a lib, then App B breaks because it hasn't been checked against the new library. I know you are a good developer who would check that, use major / minor library versions correctly etc. but there are lots of developers on the App Store. Or the fun case of updating App A, it updates a lib and then magical new features appear in App B that Apple doesn't like.
You'd probably have to use some sort of strict library versioning system where every app version is tied to a very specific library version. Are developers in general going to be disciplined enough to actually keep their apps all in sync on a specific version so older versions of the libraries can be removed? Or does this just mean every app from a developer will end up having its own slightly different revision of the lib tied to them? If it's the latter its probably not worth Apple's time adding all the complexity to manage the libraries to the App Store system.