Now right now I'm very tired, and this thought popped into my mind after reading the "Odd Wish" thread.
Normal perk point system is ENY/ENY but perhaps we could create a minute way to receive perks for a kill of bombers, fighters and vehicles?
Example: P51B with an ENY of 20 attacks a group of bombers Ju-88's (ENY 35). One bomber is destroyed in a pass, not only does the P-51 get the .57 perks, he also gets a partial perk for the category of craft he has destroyed. Let's say 1/5 (or 1/6 or 1/7 if 1/5 is too much) of that amount is also tacked on to the perk for the fighter. Therefore, the fighter would get .57 perks for destroying the bomber and an additional .11 perks (1/5) is added to the bomber category. The same could go for a bomber destroying a tank or a GV destroying a fighter. The perks wouldn't add up very quickly, but they would add up; slowly but surely.
There are two advantages to this that I see.
1. If and when a GV battle erupts, someone who has the good fortune to drop bombs on a load of GV's may have enough perks to use a good one. Although they could be content with dropping bombs, it may alleviate the whines of "breaking up perfectly good GV battles with bombs." People MIGHT be more inclined to try a GV.
2. It would give people a reason to up more low ENY aircraft seeing as they have 6/5 (7/6 or 8/7) more reward.
To put the other two "bonus amounts" into perspective. Given the same situation, the 1/6 would give the fighter .095 perks in a bomber. This is little more than 10 sorties of this same situation to receive a full perk point. (or little more than three, depending on whether all of the bombers are destroyed).
Edit: Forgot to add the 1/7. The 1/7 option would give a fighter .081 perks for a (single) bomber kill.