Thing is, that goes against what makes GoI fun. It's the idea that you can jump into a match and have a good time with people from all over the world, in a setting that a lof of people resonates with - airship to airship battle. We already, in my opinion, have enough diversity between the ships, weapons, and ammos. Building your ship from scratch would be nigh impossible to balance in a multiplayer enviroment, at least without ending up into a constricted, balanced setting of what your ship could do vs other ships, making building more of a vanity thing than anything else.
At current, the strength of the game is not to build ships, but to allow for a very social setting in a tight-knit teamwork style with airships. That's all it needs to be in my eyes.