Still have half a notion (but probably none of the gumption) to do a weird periodic social media thing:

Consider a seasonal time period - say 3 months, say a year.

Every season change, the previous season is archived as read-only and the new season's site starts empty. Everyone has to sign up again and start over. Some of the rules & processes change from season to season.

Maybe character count limits raise or lower. Maybe every post needs to be approved by some random other user. Maybe you can't use the same 3 words in the same order more than once. Maybe you can only post sounds. Maybe all the text you post gets automatically converted into kaleidoscopic imagery via an algorithm.