I think since you can hold 2 main weapons you should be able 2 hold 2 weapons, 2 armor, and 2 Vehicles. And have Achievements for stuff like that.
The idea of having two of each loadout weapons mateys and ships or whatever they are called in there mutual games is a idea that has been brought up before i believe it was shot down also. But why do you want so many achievements for everything. They already have so many achievements in the games that it will take most people a year or two down the road. Main reason people want achievements is for skill points favor points and the gold which there is plenty of ways to earn those without adding achievements to every section of the games.