The problem with solar is the lack of energy density obviously and like you say, mention the word 'battery' in a accessory and folks get turned off.
Both also have the problem we've mention i.e it adds weight and makes your device look bad. The reason I'm thinking about developing this is less about recharging devices and more about doing away with chargers altogether.
Would people pay for something that's better than wireless charging and does away with chargers altogether? Assuming battery and solar technology gets to this point in the future, quite possibly. Then again, the folks at Apple and Samsung are probably already on it.