The Dispersion Field suggestion shouldn't be too terribly hard on targeting, since the ship in question goes from taking damage as normal to fully immune to damage. Further, since the damage taken pool is decreased by a fixed amount every 0.2 seconds, the total period of invulnerability is known the moment it becomes immune to damage which might make it easier to determine whether a given ships shot would be wasted or not. Now whether that defensive mechanic would feel good in play is another question entirely.
The Damping Field would be much trickier, but depending on how armor is handled for targeting, it could be possible to convert the Damping Field into armor for direct comparison. But planning enough shots to kill before switching targets would be much harder. Then again when I made those suggestions I was thinking of only the biggest of the big using them (Golems, H/Ks, Mothership), so the inefficiency in targeting would be less important.
My understanding though is the targeting stuff is already so tight that even tiny changes to it have a massive impact on performance.