Yeah a feature like that would have to be built by Fizzer (the single developer of this game). If you want him to make something like this, the suggested pathway is to create a Uservoice: https://warlight.uservoice.com/
Once you make the Uservoice, create a forum thread linking to it (and maybe share it on Discord) so people interested in the Uservoice can find it and vote on it.
I think it'd be cool if we had something in the top bar telling us how many accounts were last seen less than 15 minutes ago, even if the number were approximate.
Absent first-party development of this feature, there are ways that someone could achieve this with a userscript but it would create some load on the site and probably not get great data. (But could maybe tell you how many people within, e.g., the active strategic community, had been active in the last 30min or 1h.)
Right now, I can't think of any good way to approximate current activity. You could see how active Global Chat is or check the most recent Clan Wars time slot (https://www.warzone.com/Clans/War?ID=5&Timeslot=1053
) but both of them have so much noise and effort required as to make them useless as proxies for gauging current activity.
Edited 9/2/2021 01:01:13