I saw it mentioned on the erlang mailing list: http://erlang.2086793.n4.nabble.com/New-EEP-draft-Pinning-operator-in-patterns-td4728380i180.html#a4728685
I quote:
The main thing that the team focused on was trying to find a model of static typing that could work in practice for real Erlang code (of which WhatsApp has a lot) - one that could give you quick feedback (even in the editor) and complete certainty that all checked parts of the code had no type errors (thus not like dialyzer). As you may also have heard already, this direction was put on ice at the end of 2020, because it seemed like it couldn’t provide a transition route quickly enough. The project continues, but for now focusing on incremental improvements.
