The 'Lighter' Side Of The Force
The theory makes sense. Like you mentioned though, there is the question of how Qui Gon's lightsaber made it to Obi Wan's hut on Tatooine. It's unlikely he had much time if any to grab anything from Coruscant before heading to Mustafar to confront Anakin.
I like this theory a lot. I do wonder if it could be a synthetic crystal or a black market crystal. Didn't many Jedi lightsabers become collector items for the elite rich?