The big issue I see with Nix is that it's solving several related & very complex problems, and isn't doing so at a particularly easy level of abstraction. It's a PITA to package software that isn't using an already-supported build system. And mixing versions is messy, instead of just `[ package1="versionA", package2="versionB", …]` sort of thing with a lockfile to convert versions to immutable IDs like commit hashes you have to specify which commits of nixpkgs had each version and then do something like `nixpkgs-versionA=GIT_COMMIT_HASH_A; nixpkgs-versionB=GIT_COMMIT_HASH_B; [ nixpkgs-versionA.package1, nixpkgs-versionB.package2, …]`. There are lots of other "warts" like that, of varying levels of annoyance.

In practice every software needs a particular version of a library. Even a minor upgrade to that library might, and will break it. In an idealized world it should not happen, but here we are. In a world that we setup whole containers so that we can run software.

So no. Shared libraries do not work in practice. At all. It should be straightforward, but they just do not work.