I actually tried this very early on in development. Let's leave fighters aside, since they're conceptually flying "above" the battlefield, so wouldn't be affected.
Turns out in actual gameplay, this almost never comes up. (In large part that's because a ship firing its engines is moving away from whatever those engines might potentially hurt.)
But in any case, it'd stop frigates from sticking their noses into the engines of your Onslaught without their shields up. More fancy than anything else =P
Honestly, how many times have you seen that? If the frigate is in the Onslaught's wake (already pretty rare)
and it doesn't have shields up, it's got other things to worry about.
Not that this isn't a cool idea - it is. Unfortunately, due to how the game works, the "bang for buck" ratio on it is approaching zero.