This is salient given policy moves by the CEO. My thoughts:

-most of what you need is basically something similar to Facebook Groups (nowadays, I bookmark Facebook Groups for the 3 groups I follow, and skip the main feed, which is basically all ads and random memes these days)

-you need a platform with mass adoption - FB got it w/ free accounts back in the day, connecting old classmates or whatnot. So a new platform would need to be free for average users

-simple signup - single "Server" - i.e. can't have the weaknesses of individual forum server software or even mastodon/federated solutions (not enough users, hard to setup)

-some way to monetize - i.e. the sins of Facebook can be traced (in part) to reliance on ads to monetize. so maybe charge for admins who want to set up their own group? It would be be an order of magnitude less income than Facebook but maybe sustainable if you keep the scope of such a site/service small.

The younger gen these days use a lot of discord, older gen uses slack, but the way they are set up with individual "servers" seems clunky to me, and no web interface but it's relatively close.