There is already a rule in place to represent that, Horizon, all H and R attacks are at -1. That's all they need.
Against a nid escort, you need a 5+ to do anything under these new rules.
PLEASE understand that when i make this argument, you are taking away strength from assault boat heavy fleets (SPACE MARINES, dark eldar, chaos, etc) and giving it to escort strong fleets (Eldar, Tyranids).
So unless you can justify giving Tyranids, one of the strongest fleets in the game who (evidently) can use campaign upgrades (since they removed the restriction from the WIP pdf), and have access to more ordnance then any other fleet as it is... NO this should not be implemented.