They are hyperlinks, there is nothing unethical about sharing them.

that or create anew

Not sure about that, it could end up being counterproductive, I mean, reddit is full of spam, if there’s no good antispam feature here you could ruin communities with a bot copying content.

Not to mention that if someone on reddit realizes there are bots copying content, they could even spam the subs on purpose.

I believe it would be better to do it manually, copying the source in case of links, not copying text post, that wouldn’t be honest IMO.

There are a few Mastodon bots that do that for some prominent Twitter accounts. I suppose it could work for links here but wouldn't really make sense for text posts.

The best way I think is to have specific set of servers with the sole purpose of cataloging. Reddit grew to it's size organically, and the same would have to happen here for it to actually work. But I think for just internet historical purposes and to drive content here to have something searchable to add some utility early on is absolutely worthwhile.