I have only gotten to experience the vespers of that deeper engagement which was a combination of web forum with on-topic threads that you could follow via email for mobile posting, and reply to in kind.

I think Discourse is the platform of choice right now, and I'm going to get one going for my immediate family / f2 network rather than a public one. If I did a public one, it would be one where each user could only subscribe to it at $5+ per month, then graduate the cost of new sign-ups and monthly costs to be 5+<monthly average users> for each new user, specifically so I could pay server hosting costs, market the site for the target audience somehow (users willing to prioritize long-term reputation and effort posting and pre-eternal-september netiquette) and pay one or more mods to keep the site behaving and on-topic for each given forum.

We can have the flamewars section on politics and religion, we can have the skills section on getting advice from industry experts in their own vocations, we can have the web1 section for hamster dance, retroweb and retrocomputing hubs, web2 section for flash revival and homestarruner and fark and reaction images, and we can have web3 for doing 'people of walmart' but for algorithm meat puppets from social media and short form brains and chat-only sites.

This magical site would have RSS feeds for every thread, easily enable web/mobile posting, support email mailing lists, make it easy to split a thread as conversation diverges, and enable enough social features to have signatures and home pages, but discourage passive likes / empty internet calories. So a mash-up of discourse, LKML, XenForo, and phBB.

The Tech is not the main problem, its the finding of each new user, the site as designed above would stay pretty small as is, it needs to be able to grow to let new users in without growing so far that the core user base dilutes away to let in the 'sociopaths' and the 'groupies' that the old 4chan 'how a space gets ruined over time' edgelord meme images show.