You have done a lot of work and the result is really impressive. If we compare it with Flarum, their obsession with JS has led to the fact that no design themes have yet been created that differ from the default one. Modification usually comes down to changing colors, because without JS knowledge it is difficult to seriously change something. Flarum's weak point remains its poor integration with Laravel.
I like the Waterhole, but I won't buy it for two reasons. Firstly, you are developing alone and if something changes in your life plans, users will be left with nothing. Secondly, $100 annually for updates for a project that does not bring me money, this is unacceptable.
I think it was more correct to first form a community around the new engine, then monetize it. A little activity seems to show that things are not going well so far. In any case, thank you for not giving up the idea of creating a user-friendly Internet forum for many years. I've been following your activities since the days of esoTalk: the timeline feed and minimalistic design are truly innovative things.