You could probably create a list of sites that have a paywall anywhere but I'm not sure if that would really provide a huge benefit.
For me, if a site has a paywall and I'm not willing to pay for it then I'll often read the comments to determine if I want to consider paying for it (normally only after I run into the same wall multiple times) or if I want to go looking on the internet for other reporting on the topic.
Actually, the guidelines say: "If they'd cover it on TV news, it's probably off-topic". And also: "anything that gratifies one's intellectual curiosity" is OK.[1]
Long-form articles on news sites usually have much more intellectual content than TV news.
Even if it's not exactly where I'd set the dial, it's probably a rough average of the community, and the consolation prize is that controversial stories rapidly bury themselves.
Hell, I'll help build the feature its that much of a nuisance...