Here's a Fusin gear hub I did similar, except I retained the fixed axle for easy swingarm mounting. I used a piece of pipe as my output shaft that fits to the sun gear. It's that long so it extends out of the housing which is now stationary. Output shaft is supported by bearing on the end. The spinning rotor which I affixed some blades, which turns the unit into a centrifugal fan with input at the wire side straight at the exposed stator and windings.
Yes, 2x rated power is a good estimate if you get fresh air in. I elected to dump the planetaries in favor of a #25 chain. It works fine, but project set aside for high power interests. Geared hubbies still have the problematic issue of thick and/or cheap steel laminations due to the pursuit of cheapest solution instead of a better motor. I'm working with a factory to end that though with a proper geared hubbie leaving mid-drives the solution only if you're going airborne or require multiple speeds. A high efficiency motor in a geared hubbie with proper heat dissipation is long overdue, and I'm sure the motorcycle companies will come out with a high powered version (maybe even with 2 speeds) in the not too distant future....Come on batteries, it's time to deliver what was promised in '08, '09, and '10.