Interesting, as a LambdaMOO user -- which borrowed many of the forms of TinyMUD but in its own lineage -- I wasn't aware of this earlier form of "page";

On LambdaMOO (and LambdaCore) whisper was for in-room communication and "page" sent a message to someone privately anywhere on the MOO. In reality nobody used whisper. I never knew there was a form of page that didn't carry a message.

Things like your "mutter" were easy to code up in MOO, and I recall people doing things like this, but it being seriously seriously frowned upon.

BTW you might be interested in my project https://github.com/timbran-project/moor