I think that the Internet Archive is doing just fine in terms of being used as a way to save important parts or contents on the Internet, there's probably someone out there that's already doing what you're trying to propose and I think that it would be a really awesome thing if there really is someone doing it and not just some threads on the forum but the whole forum itself and when it happens, it will feel like you're exploring the forum itself when you check out on the preserved forum in the future that this forum is really going to go away.
You're probably talking about the Wayback Machine, accessible in the Internet Archive. If that's so, you'll have to index pages of the internet first on the Internet Archive before you could even access them at a later time, and I do not need to tell you how little the amount of people in here who would go so far as to index pages of the forum just so they can check it at a later time, especially with third-party notifications being a thing in this forum already.
So yeah, the idea's good don't get me wrong, it's just boring and cumbersome, plus the Wayback Machine's facing some of their own shit too as of late, just watch SomeOrdinaryGamers' vid about the Internet Archive facing shut down and shit.