I feel like this would be spotted and stamped out immediately. Everyone's eyes are on Threads right now; astroturfed content might sneak in on Mastodon, where regular Threads content will be mixed in with the hypothetical astroturfed content, but here on Lemmy there will be little to no Threads presence due to lack of interoperability, so every single Threads account that shows up will be noticed. It's already super visible when Mastodon users show up due to the weird formatting issues that happen due to the lack of support.
I just don't see an astroturf campaign as being viable unless Threads implements community functionality, which seems pretty far out when they're only now implementing basic federation with Mastodon.