I think it would be useful if there has been this feature because it would allow you to easily check which players are playing on which server without having to start minecraft client.
I mean, what use would it be other than seeing if your friends are on, but even with that you could simply ask them trough a msging app like discord, skype or teamspeak
Not everyone uses msging apps like discord/skype/teamspeak for many different reasons (some don't want to install, others like me don't agree with EULA...).
It should be a super easy thing to implement as the functionality to show the names of each online staff member when hovering over the online staff number is already there, all that it would take is extending that to players and binding that onhover to the online players number. Say I got bored of the modpack I was currently playing and decided to try something different, if this were implemented then i could open the stats page and then slowly move my mouse down the online players column looking out for any familiar usernames (people i know from previous servers but who I don't necessarily communicate with outside the game), then I could base my decision of what pack to play based on who else I know is currently playing which modpack.
I see your point, and I complete agree, nothing better than being able to play with old friends that you don't have on social platforms!