I think it would be cool, but a little OP for farming dun powder. Think about it. You're far in the game. You have full diamond armor with full blast resistance on every piece. You make a creeper trap, or you get a bunch of them. Then, you do that trick, getting close to it, it explodes, but doesn't really hit you, though it if does a little, you have full armor, so it's ok. Also, this would make it way too easy to get rid of creepers.