This proposal started as an X-Wing Only Thing© (after reading some of the "fix the X-Wing threads") and it could be made to have wider application (though I like it better as an X-Wing only modification, personally.)
The mechanic being something along the lines of: the modification card is placed (horizontally) above or below the pilot card to signify Double-Front/Double-Rear. A number of shield tokens equal to the current number of shield tokens on the pilot card are placed on the modification card. The opposite arc is treated as having no shields. If the shields are re-balanced, the shield tokens on the modification card are lost (card is placed beside the pilot card) but the opposite arc may benefit from the protection of any shield tokens on the pilot card. I see this as costing an action (ACTION: header), but remains until changed.
Balance issues: As the shield tokens on the ship card are worn down, the benefit is largely reduced/eliminated. This is something likely to be used on turn one or two (i.e. preparing to engage.)
There would need to be a clear mechanism for determining if an incoming attack hits the doubled-arc or merely the side (normal shield - no doubling effect) or the "naked arc". My initial thought is that a line from center post to center post be used for this. Roll a red die if it cannot be determined/ambiguous. (Hit/Crit it is the attackers choice, Focus/Blank, it is the defender's choice.)
Cost would be fixed if X-Wing only, or based on a ships shield strength, if open to other ships.
Thoughts/Ideas/Tantrums?
RogueMorgan