Signal began rolling optional usernames and will hide phone numbers from new contacts by default. Existing chats keep working; the change is about discovery, not encryption. That is the narrow version of Signal usernames.
The person this changes first is anyone who shares a phone number only because a chat app demanded it. Signal is who the reporting names, and that is not a claim about every rival in the same market.
I am not adding a result the report did not state. A pilot, a pledge, a filing, and a product you can buy are different events, and Signal usernames is only as far as the first sentence.
If this touches something you use this week, act on the opening fact. If a later note from Signal disagrees, keep that one.