I would not pay because the content on HN isn't so specialized that I cannot find the community elsewhere. Furthermore, trolls are easily identified and ignored, like SPAM.
However if there were a subscription, I think you need to think about the value of this community. Charging just posters would unleash a backlash by the most active members of this community. Their thought would be, "why would I PAY to participate in a community when everyone else can obtain the value of my knowledge for FREE?" Using the email analogy again, if everyone who wanted to email me had to pay $5/year, I would probably receive no spam, but more importantly no emails at all -- not even from my mother who would just use a cheaper substitute (phone).
However if there were a subscription, I think you need to think about the value of this community. Charging just posters would unleash a backlash by the most active members of this community. Their thought would be, "why would I PAY to participate in a community when everyone else can obtain the value of my knowledge for FREE?" Using the email analogy again, if everyone who wanted to email me had to pay $5/year, I would probably receive no spam, but more importantly no emails at all -- not even from my mother who would just use a cheaper substitute (phone).