Not a Flarum developer, but I develop with PHP professionally: PHP is not capable very well of long running processes and the existing solutions are not very efficient. You may always need something like pusher or a free alternative for self hosting like soketi. The only way to achieve this I can think of right now is to use some kind of polling which would mean that you have consistent send requests to your webserver which is going to increase the load to the server. The actual amount of that depends on the implementation.
