Thanks John, this is something what I've searched for but didn't find. You did not use the planetary reduction anymore I assume. That's sad, since it's made so well, except for the weak plastic gears, but these can be replaced.
I'm not willing to charge the hub with air. This way dust could get in (which is what killed my tongxin drive) and it would still be poorly cooled since the stator lacks of cooling surface. What I want is to thermaly connect the hub to the stator by 3 alloy sheet pieces with thermal grease. I did not d any real calcs yet, but from estimation I can tell that heat dissipation should be increased by 3-4 by this.
The stator laminations don't look that thick. I assume 0.6-0.8mm. Could be well enough for 1800rpm i hope.
About batteries: We arrived at 270wh per kilograms this year. Compared to my cheap lipos, which get about 125wh/kg, this is more than double. There is an increase of almost 100% within the past 5 years. What should we bother about?
I'm waiting keen for 2-speed hubs. But I guess it will still take some years till they come to market.