As an alternative to buying longer booms, what about making new larger center plates that will effectively increase the length of the boom by 50/100mm? Then for the smaller size, the booms would simply get pushed in farther.
I love guys that think outside the box. From a weight and expense perspective, it would probably be worse, but from an area perspective, it would be a great way to disburse the weight of multiple batteries.
I bet the weight difference would be negligible. Also the cost could be about half. ~$400 for two plates vs $800 for new booms. I think there's a way to design it so all the current gear would still fit in the same places. And you're right, more area for batteries, esc's...etc.
I think I'm going to have to break out my high school math (which is not a pretty sight) and calculate the weights involved -- I remember have deep suspicions about how the rapidly the circumference of a circle increases with respect to its radius when I was studying calculus (back in the Dim Times). But it's an interesting idea nevertheless. Andy.