Development of high-quality forum software is something I have considered undertaking.
Hypothetically, If one were to offer something that was hosted and provided a trivial one-click sqlite export facility, would HN generally agree to participate in that sort of ecosystem? A public webhook could be exposed so that enterprising users could build their own replicas or other event-sourced systems on top... Account management would be simple and robust. PBKDF2 scheme over unconstrained passwords with optional 2nd factor of user's choice. All account facts aside from the primary key, email address, hash, salt and iteration count would reside in the public domain, so compliance with regs simply involves allowing the user to remove these items from the system. 1 simple button with a "are you sure" and that's that. The only traces are everything you knowingly placed in the public domain.
So, we are just talking about plaintext/markdown here, right? Hackernews comment-tier feature set, but threads stay around forever like reddit? This really doesn't seem like rocket science. Maybe add a tagging/labeling system like GitHub has so that users can quickly go lateral on related topics or comments?
I feel you could take what HN has and add another 5-10% unicorn dust on top and have the best forum solution on earth. Keeping the tools heavily constrained and simple is the key to success here. Twitter is a good example of both. Look at the quality of conversation on HN. Arguably unparalleled as-is. What if these awesome conversation threads just kept going after the initial 24h? Wouldn't that be incredible?