The post reads:

making the three modules into just one: Tie::Hash

To me this means merging Tie::Hash, Tie::StdHash, and Tie::ExtraHash into a single package. That can't be done because Tie::ExtraHash uses a different internal storage, and Tie::Hash implements a CLEAR method that is useful for subclasses that don't use the same storage as Tie::StdHash.

Similar things are true for the other modules. Tie::Scalar is maybe the only one that could be merged, but arguably the current Tie::Scalar package serves no purpose.