>>pg+(OP)
The way to save HN from its own success is to take it to the next level. You need to spin it up into a commercial enterprise. Improving the quality of HN, as it stands today, requires expenditure of human effort, either in the form of professional moderation, or some sort of AI-ish enhancement: pruning of message threads, credentialing users in more sophisticated ways, finding ways to bubble up story submissions that otherwise get lost.
No doubt some will find the commercial option distasteful, but I think the pure crowd-sourced option has run its course. Commercializing HN would allow further expansion, for instance splitting it into several areas of interest. Stackoverflow/StackExchange is a model for this. There is much value that can be added on to HN, as many Hackers have shown in the past with various projects.