We are wanting to change. See the public discussion at our GitLab. FluxBB is an unmaintained dead-end and it's just a question of time when it breaks. The migration path has to be well-developed before we do it though.
In that issue, you can we did an evaluation of all obvious alternatives and it really comes down to Discourse. It really doesn't seem to have any modern, maintained alternatives.
So yes, it will happen. Question is when.
The easiest way I found is to use caddy which already has tailscale support and will fetch a certificate for hosts behind your tailnet address.