That's not really the same challenge at all though. If golds are generated with the level, you get experience from exploring, and lose it by making explosions and environmental hazards out of your vision. If they're generated by killing monsters, you get experience from killed monsters, and lose it by killing them with environmental hazards, killing them out of sight, and fighting groups of monsters.
Not that I think it's a bad idea, but I don't think the flavor fits as well as something like Angel of Undertaking, where they leave $oul Wisps or something instead of treasure. It also sounds absolutely brutal, since you'll have to immediately rush to every corpse if you don't want to lose experience. I know the numbers can be balanced, but if an experience pile starts at 150% and degrades 1/15 per second, then it drops below 100% after only 6 seconds. Even if the degeneration is reduced to 1/30, you'll probably be getting less experience unless you're playing a melee build.
Anyway, here's another idea, Angel of Tunnel Vision:
Projectiles always miss monsters and barrels other than their intended target, although shotguns and splash damage work normally. For monsters, this means they will never injure each other or blow up a barrel, unless it's a former sergeant firing, or some explosive projectile hits the player or a wall. For the player, your projectiles won't even roll to-hit except against your target: if there is a monster or a barrel under your targeting X, that is your target, otherwise the first monster or barrel the projectile encounters is your target.
Mobs of enemies are significantly more dangerous, since all those former humans will be shooting you instead of each other. Even worse, if your chaingun misses the first guy, you don't get the consolation prize of it hitting the guy behind him. On the flip side, you don't have to kill five mancubi for every hit you land on that arch-vile.