My idea is: It would be neat to have a way to see who else is currently signed in to Mautic - kind of like you can see who else is viewing a document on Google Docs or is editing a Trello card in Trello.
I think these groups of people would benefit from this idea: Admins, who need to do a quick restart of the server and don’t want anyone to lose their session data.
Why I think they would benefit from this idea: They can see that they should not restart while someone is online.
Are you willing to work on this idea?: No. I’m probably too dumb 
but I suppose it would be down to whether Mautic has a way to keep track of the number of active sessions.
What skills and resources do you need to explore this further? Time and patience