Why don't niche subreddits just start web forums up again? It's simple enough to pay the hosting bills with some sideroll ads (that clever admins could even sell at a premium, thanks to their highly niche audience). Of course, today's Reddit mods would have to reskill a bit to run a forum, pick up some admin tasks, etc. But if they're already donating tons of free time to moderate that might not be a huge deal.

I use maybe 2-5 subreddits at this point because Reddit has rotted out so much. At least half of those are shutting down permanently as a result of the API changes, and the other half are participating in the blackout. I don't need a shared account across all of those services. In fact, I tend to visit subreddits individually anyway so I don't have to guess about the context of every post.

None of my favorite subreddits rely heavily on photo posts, which keeps hosting costs low. In fact, I notice a strong association between quality and text-only subs, likely because it keeps the lowest quality memes away.

It might not work for every subreddit -- I don't anticipate the denizens of /r/funny would embrace a web forum -- but for hobby, book, and series-related communities, web forums have been around a whole lot longer than Reddit. Reddit only took over because it was marginally cheaper and easier to host; if mods lose their useful mod tools and power users lose bearable and efficient methods of browsing, forums start to look mighty attractive again.