This is a frustrating change being proposed and I don't like how powerless I feel to stop it. I even started donating to Signal because I support what they have done but it will dramatically limit the usability of the app. Many people sign up for Signal and then never check it and so it was convenient to be able to send a insecure SMS message to them instead.
The only possible benefit to this would be to break their dependence on using phone numbers as the way to sign up for accounts and possibly provide a reasonable way to export message data.
Otherwise it just feels like the wrong decision and a reminder that Signal is not a community driven project but subject to arbitrary changes and provides no way to fork or disagree with the project lead as can be done with most free and open source software.