The 35% Attacking Rule has been re-added. This is a galaxy setting, defaulted to enabled.
You cannot attack players under 35% of your own NW, unless they attack/op you first. If they do, you can attack them for 48 hours after their action against you.
During wartime, 35% changes to 25%.
Huge thanks to @Luker8969 and @Daffy for helping me test this one. 
Enjoy!