It's a solved problem technically, certainly, but assuming all of the relevant source code will always be available ignores some social and legal issues.
One issue I was thinking of was companies that distribute code in binary form only, not ASTs or anything which could be used to steal their thoughts. The other issue was in reverse, however: A binary-only package is unmaintained and lists as dependencies hashes that no longer exist because they're the hashed versions of ASTs that, for one reason or another, the compiler won't generate, even if the source still exists. Versioning and archiving would help this case, at least.
It's a common approach in language design to require this though. Rust has made very similar design choices due to its (current) lack of stable ABIs. IIRC some hash of the compiler version is included in built libraries and prevents accidental linking. You need to rebuild the world for every toolchain upgrade.
