That said, I doubt we'll ever escape towards subscription-based social media models due to the prohibitive costs of CDNs, bandwidth, and storage for video/images. But I suppose it's a question of ends: do we want everyone on social media?
If you can live without video and images, you could comfortably host even a very large forum (on the order of the top 10% of subreddits by volume) with only a $5/month VPS, as long as you made it serve static pages and were judicious with your tech stack. The cost of hosting text alone wasn't prohibitive 20 years ago, and it's even less so today.
That said, I doubt we'll ever escape towards subscription-based social media models due to the prohibitive costs of CDNs, bandwidth, and storage for video/images. But I suppose it's a question of ends: do we want everyone on social media?