First off, A lipo cause a burst fire, that is hardly an explosion. These fires create a violent flame but die out very fast as well, as the the chemical fuel runs out. That being said I see no good reason to put Lipo in a heavyweight other than a weight advantage.

I think as LiFePo4 develops, the market for LiPo will steadily die out. Batteries need to become more stabile, and in the power to weight ratio LiPo wins for the moment, but that difference will decrease as production and research improves.