I’ve heard certain clients or servers are able to spot crossposts and reposts, and mark them as crossposts/reposts. I definitely know that the app I use does not.

I think it’s doable. It’d likely require hashing posts so that Lemmy apps can keep track of those hashes.

Also, smaller servers means that it’s easier to spot criminal communities and boot their asses. Also individual servers can be cracked down on for hosting evil content, without all of Lemmy being destroyed.

Voyager also work good.