There is no reason why an attacker couldn't do that already. Consensus allows it. An attack like that would probably come from a govt because it would require law enforcement involvement to follow up on the threat. As soon as they get one node runner it would be obvious to everyone who the attacker is. The data could then be pruned before they could go after any significant number of node operators. No one is forced to store any data that is in op_return or witness if they don't want to.