That's an interesting point that the parent post made - we probably shouldn't be thinking about these devices as just underclocked versions of first world devices. I think that you could design a positive user experience with all of the restrictions that I listed above (not ideal, but still positive), but it's not going to be achieved by disabling features of a super phone/tablet.
Something like a Pixel-Qi screen would be beneficial in cloudless desert climates. An entirely reflective screen might be even better. City dwellers have no need to think about this, but there are many parts of the world where the outdoors aren't illuminated at night. If people are about after dark, they are likely to already have their own source of illumination with them.
A thicker, more robust form factor that's waterproof and buoyant might be beneficial for other climates. June through September is India's Monsoon season. That doesn't strike me as the friendliest climate for an iPhone.
In other words, what really sucks about smartphones in the developing world right now? Also note, that this is very likely to be different for different markets, and that the developing world is not one market, but many.
For one thing, I suspect that there are places where charging every week would be much better than charging every day. The device should also be designed as a standalone device, and it would also need to be backed by cloud infrastructure situated to create favorable latency and bandwidth for each market.