Did you not see the pictures posted above from bird strikes? If a bird could cause that much damage to an engine, imagine what would happen with the high speed blades hitting hard plastic and metal. Add in the hot flames from the burning Lipo, which would cause the engine to overheat and immediately shut down, and you have a plane that would be in serious trouble, especially on take off.

Besides, not all explosions are violent. A very hot sudden burst of flame is also considered an explosion. Even if it just smolders, the smoke given off could extinguish the burners in the engine. Not to mention the collateral damage the blades will do when they break apart from the impact. They are traveling at a very high rate of speed, and can shoot through the cabin, rip though lines and cabling, and the sudden loss of balance in the engine could cause it to break off. Frankly this is not something I would ever want to hear happen.