For anyone interested, there have been some progress on this topic. As a start:
https://github.com/NixOS/nixpkgs/pull/88714
Is a baby step towards an openjdk rename, should be OK. Renames jdk to point to jdk14, while every derivation that uses jdk without an explicit version suffix, now uses jdk8 explicitly, in order to avoid mass rebuilds and to make the review easier - by relying on the fact that no attributes were really affected.
This one:
https://github.com/NixOS/nixpkgs/pull/87848
Is specific for llvm - just a single package that starts to use now the latest version of llvm (if possible, for darwin that wasn’t possible).
There’s also:
https://github.com/NixOS/nixpkgs/pull/88195
Which renames libressl. Using ofborg I’ve checked there that nothing brakes so I think it’s good to go.