That's because the BMX hub already has an SS driveshell as far as I know, it's just a shorter one, so you wouldnt be able to upgrade it to anything. The internals are exactly the same in both hubs, and my hubshell is a standard ISO hub, it's just got a shorter driveshell and axle in it, therefore I SHOULD be able to just take off the driveshell, and put a longer one on (standard SS one) and a new standard 135mm axle, and it would work. What I'm saying is that the MTB hubs have buy-to-order upgrades availble, but the BMX ones dont. The internals on both hubs are exactly the same, so why can't it happen?