Could it? Yes. Should it? No (My opinion). Would it? No (I highly doubt it).

As for your interior question of why it hasn't been replicated for other topics, I don't think it's simple enough to replicated. HN isn't monetized traditionally so there isn't a successful business model to replicate unless you include the entire company of Y Combinator.

Probably, but I hope not. HN has a community of people really knowledgeable in a lot of areas who really try to maintain a high level of discourse. I fear that the priorities of monitization would alienate many members. I couldnt fault PG for wanting HN to pay for itself, but I hope the community itself would justify its remaining as it is.

HN isn't being monetized directly, but it is bringing tremendous value to YC. It's might even be their most valuable asset.

At the very least it could be made into a business on donations alone I am sure.

PG has a great thing going here that is far more valuable to him than money. He isn't aching for food on a daily basis so I doubt he'll ever dream of jeopardizing HN the way it is.

Why don't all the mini sub Reddits count?