Of course. You can't MITM all the traffic to the site. But if hackers are targeting a certain security-conscious user, this standard will give them another tool

Of course. You can't MITM all the traffic to the site. But if hackers are targeting a certain security-conscious user, this standard will give them another tool! This new layer will make the security better for the average user, but it will enable attackers to make a website look falsely patched in a MITM attack.