First off, I like the idea. But there is no reason to limit the gun effectiveness in any other way than by the formation itself. Meaning, the effectiveness of the guns will vary depending on the formation.
Also... I would like to see crosshairs of where the other bombers in your formation are going to drop when you are looking through the bombsight. After all, you are really playing the role of the bombardier in all 3 planes at the same time.
The formations could be changed in flight with something as simple as a .formation command. Here is an example of what I am talking about.




Some may say that being able to see the crosshairs for the other bombers is a little too cheezy... and I can see that point. But even if you didnt have the crosshairs for the other bombers on your screen, you would know just based on which formation you had selected about where the other two are going to drop, and with practice, would be able to pinpoint several targets in one pass.
If variable formations were implemented, it would also be nice to be able to select which bombers in your formation will drop their bombs, and which wont. Just another simple command really. Something like: .drop 1.2.3 would be for all 3 bombers to release on command, while .drop 1.3 would be telling just bombers 1 & 3 to release. Because by spreading the formation, you may have the need to keep one of the bombers from dropping, since it wouldnt be hitting anything of value.