I know that powerplants are realy possible to implant in the game. But I guess they take a shield slot, not misc storage. However, parhaps it's possible to change, I'm not a programmer.
I think this would be a nice idea. Expecialy in creating of specialized anti-cap bombers, which would fall under fighter guns like flies.
As mentioned above, capacity for powerplants should stay as it is, to prevent double SN bombers
But tbh, I think they wouldnt be -that- overpowered in certain cases - Barghest, Waran and Fafnir are already epic fail against fighters, double SN would just improve their ability to fight caps, if its the Bomber vs Fighter balance you are afraid of (if its because bomber vs caps balance, ignore the article)
Regen upgrades might be nice diversity from everyday universal VIII AU fighters/bombers. But I dont know if there will be anyone willing to lose considerable amount of armor from his ship. Especially capships are very dependent on armor upgrades, since they cant -really- dodge (at least cruisers and above).
So it will end up with LFs/HFs as the only ones having them I think.