Imagine Stack Overflow, but you have some probability of not seeing the top answer. That’s pretty much what happens with federated instances blocking each other. I wouldn’t use that.

syncthing

And I’m saying you can encounter the same issue of not finding a post whether you save it or not. If you suggest saving content to reference later, there also needs to be a way to search within those saved posts. Otherwise, it’s essentially the same problem as not being able to find it without having saved it.

You would need to be able to search saved posts which would also be useful, but not nearly as much.