Sounds like a solution in search of a problem. But, you're free to add your own extensions on to x3d, if you want to give each part of your sub-assembly a "mood

Sounds like a solution in search of a problem. But, you're free to add your own extensions on to x3d, if you want to give each part of your sub-assembly a "mood" or "taste" and still have your artifacts be interoperable with the rest of the world.