I did some thinking about that and you know what it doesn't matter. We can still get our 4000mAh battery via third party vendors. They make higher capacity slim batteries already for the V10 that give you 3900mAh or so and is the same size as the stock battery. Give it a few weeks and we can get our removable 4000mAh batteries without having to add extra bulk to the phone. Win win!
There is no way to build a 4000 mah battery that is the same size as the 3200 mah battery. I have bought a few so called same size extended batteries for my N3, which coinsidentally has a 3200 mah battery. They claimed a larger capacity but didn't deliver. I weighed the batteries and they weighed exactly the same as the original, so to expect more performance from the same size/weight extended battery with the same amount of lithium is a pipe dream. The only difference with these so called same size extended batteries were the exaggerated mah printed on them.