Do you mean a block that displays for example "27 users currently in the "Salon""?
That would work yes. Preferably something like your 2nd screenshot above (messenger page) showing 'each' person who is in the chat instead of a full count though.
You may see participants names in messenger talk's title only when talk has not title, i.e. when talk was created from messenger main page, but not as block of any another page. It shows first 3 participant's names.