Many of the sites that are featured on HN are not even the actual source of information, which often gets linked in the comments. As for going more "invasive", it's that exact reason that ads are being attacked, so I wouldn't bet on that working out long term either. I also fail to see how logging in inherently leads to revenue, unless we're talking about a subscription service in which case it'll live or die by the quality of the content....or else no one is going to pay.