I don't understand why it has to be a "product" with a "market". Mastodon (and old-school forums) have shown that as long as you can cover the hosting costs of an instance, you can have social media without the bad incentives that giant centralized networks have.

The lesson of the past 15 years is that creating a "global town hall" with hundreds of millions of daily users doesn't guarantee profitability. So why not decentralize and try to go small and local, like the phpBB forums that are still chugging along?