This.
I'm one of the people affected; I am already shut out of the discussion, and when I am not on a fast unmetered broadband connection, the wait and the advertising thrown at me instead of the content that was promised feels like I am being punished for following HN links, every time.
I'm not suggesting it is a perfect solution, but a heads-up would be strictly better than what we have now.
(I don't much like the idea of copying paywalled content elsewhere, as suggested by other commenters - there are obvious legality issues, and also it seems morally dubious at best; the content provider has made the decision that they don't want non-paying customers to read their stuff, and however we feel about this, we ought to respect it - just as my decision not to pay for some kinds of content (and hence not receive that content) should be respected as a valid choice instead of being punished.)