It's fine to post archive links in the comments, but it's important that the original link be at the top level (unless it no longer exists on the web).
("Please submit the original source. If a post reports on something found on another site, submit the latter." - https://news.ycombinator.com/newsguidelines.html)
(Perhaps the "right" way to do it for HN would be to post the original url even if its paywalled, and add a comment with an archive/paywall-busting link as well?)
Or did I miss something you meant?
In your roadmap for "more formal support", perhaps a way to pin the original submitters first comment to the top might be worth consideration? So that a comment providing an archive or non-paywalled link doesn't end up buried by the top comments in the following discussion? That could also help out with the occasions when "editorialising" the title is a thing the submitter would otherwise be tempted to do?