The feature is currently only testing with a small percentage of users, but it seems like a sensible addition that I bet will get rolled out further. For privacy, users with public accounts can go to their Settings to turn off the ability for others to reshare their posts. Even if you don’t have the reshare option yet, you can still find the privacy setting now. Then again, people could still just screenshot their posts. In fact, this was such a common activity that it likely encouraged Instagram to formalize it with resharing. Instagram was rumored to be testing a Regram button for sharing feed posts back to the feed, but that appears to have been false, or at least never rolled out.
