I don’t think that need be the case if it were possible to assign a primary link to a new post:
$discourse/new-topic-link?link=$link
Which would presumably forward to the thread if it already exists and use the existing logic in the embed admin. Maybe with templates?
I guess another way to solve this is to search for any posts that refer to the link in question and surface any matches as part of a site-wide conversation, rendering directly in the page via SSR. This might be equivalent given that the embeds are view only anyways. The most obvious issue there would be choosing which thread to send the user to when they want to participate.
edit: if I can figure out how to search posts by link content