neptronix said:
but the internal controller worries me a bit ( internal controllers typically fail inside hub motors early );
The main reason they fail is heat damaging components. As long as the design of the whole motor/controller unit is created around how much heat it can dissipate, and it monitors that and limits power usage based on that, alerting the user to heat problems as well (so the user knows why power is being limited), they could last as long as any other motor/controller system.
Eventually, electrolytic caps will fail (they only last so many hours at such and such a temperature/etc), requiring controller repair or replacement, but good quality caps with as high a rating for that as possible will probably make that timespan as long or longer than the device it's part of will be used, anyway (for the majority of users).
Now, if they stuck the battery in there too....
Of course, the typical system like this is made at the lowest possible cost and probably has no thermal monitoring (at best, an emergency cutoff that just shutsdown when it has already reached a too-high temperature), and probably no power rollback even if it does any thermal monitoring, probably no engineering to determine and maximize heat dissipation / requirements, etc. Certainly doesn't have caps made to handle the heat, etc.
The Ultramotors (stromer, A2B, etc) seem to do pretty well for this type of system, but I think they still needed better thermal management. (but I don't actually know what failure mode any of them ever had; the controllers are potted pucks, and the systems are proprietary controls/interfaces, so it'd be hard to test just a dead controller to figure it out).