OK what about the coaster (hub) brake?
Less likely to be knocked out of shape than discs, and similarly low-maintenance, rim-friendly, weatherproof and immune to spoke breakage/bent rims. And still common on bikes in India/Africa.
I've tried it. They don't work in that context. Apart from the annoying modulator nonsense "We've fitted a device that makes your brakes rubbish for your safety" here is the short version of my experience of a 'big unit' like myself using hub braked bike to tour in some real mountains.
The grease melts, and in fact burns off, though I liked the smell, and they start to screech and scream. This gets louder. AND LOUDER. Until you notice songbirds dropping dead from out the sky ears bleeding, the sheep in the valley below starting to stampede and the shepherds and farmers peering into the sky to find the dive-bomber their ears tell them is about to attack as the hideous noise your tortured brakes are making echoes from one side of the hitherto tranquil valley.
Then suddenly, at some critical temperature which Shimano don't publish, they fade, they fade quicker than a dimmer switch at a swingers party. If you keep applying them one of two things then happens; they overheat to the extent they self destruct and with a final scream of agony lock up and spit you off the bike or, and to be honest the previous outcome is preferable, you find yourself riding in a sudden silence, broken only by wind noise and a realisation that it is your own voice shouting Anglo-Saxon monosyllables at the universe, towards that nice low wall on the hair pin bend, you know the one, the one with the REALLY HUGE sheer drop on the other side, that you are now heading towards with NO BRAKES AT ALL.
Please don't ask me how I know this. My palms are sweating writing this as it is. I'm going to go and have a lie down now.
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