Finding the 'Paul-Graham-of-Knitters' for each community is exactly how I was thinking of approaching this. Getting those people to buy in to the concept will be a challengeIndeed. And you are competing with the likes of StackOverflow and their millions.
With Reddit, the difference is in how customizable it is. You can hit "Politics" and get a list of posts loosely related to politics. But you can't get a feed specifically for "New York Politics" or better, "New York Republicans".
Folks can create sub-reddits as detailed as they want. Some get enough traction to survive, some don't. I still don't see how your site would be different.
I may be wrong, but HN could be a business if PG wanted it to be.
And how would you monetize it? I don't see an obvious business model.
However would you agree that even HN has it's share of trolls? How does HN keep them out?
HN has trolls, despite the fact that and PG spends a lot of time trying to cultivate the commnity. There are (all too often) posts complaining that "HN is turning into Reddit"-- which ought give one pause.
I believe there are people out there who take topics (of the non-technical variety) seriously enough to fight for the maintenance of their community.
I imagine there are. And I imagine that in a large number of cases, they've already done so. I imagine there is at least one Knitter's forum successfully meeting the needs of a large chunk of the Knitter's community. I'm not really sure there is an untapped market out there.
I don't mean to sound so negative-- but there's a difference between an application and a startup. You've written some software; I'm not sure there is a viable business model behind it, especially in competition with Reddit.