Suggestion: If the world is underpopulated, tell the user about a "Big Day" that's at some specific time in the future, when they're supposed to return. Help people to coordinate to come on at the same time.
Mention the number of users who were present at the previous recommended time. If it works, it will be a large and enticing number.
The fewer users are visiting, the further in the future the next Big Day should be scheduled.
If possible, get the app to send a notification when Big Day is about to start, if the user expressed interest? I guess you probably need to be Installed to run in the background and do that but there might also be some windows calendar/event scheduling API you could access without that.
Thank you so kindly much for the suggestion, though I'm not certain whether that's something I'm personally interested in
I think there's genuinely something really charming about there being spaces on the internet that allow for occasional motes of human interaction, without pushing for increased engagement
That makes sense. Well, okay, you could raise the frequency of Big Days to lower the number of people a visitor is likely to meet when they turn up. You can also reframe it, it doesn't have to be extroverted in theme. It can just be something like... "the egg will hatch in an hour". Or "a star will land way over there". Something a player will want to turn up and see. So will others.