Hmmm. Not sure messing with the end-game condition like that is sensible. At the very least "If this would cause a draw" rather than fixing every draw condition; otherwise "We're stalled out? And this is the last turn of the stall? I cast this and win with stupid unfairness."

And, um, my opponent casts one too and the world explodes. Probably resolvable, but I have NO idea who has priority during resolution of the game ending.

Nice flavour though. My suggested simplest fix would be "~ deals 3 damage to each player. If this would reduce you to less than 1 life, you have life instead"

If you use this, the idea was to make a suicidal deck, probably using Sulfuric Vortex, Flame Rift or Earthquake. So it would be weird that you couldn't finish the game with those cards and instead had to wait until your upkeep.

Aside from that, I thought the other ways to draw a game (Zaping a player with 1 life if you have no cards in library or creating an infinite loop) were pretty rare. I didn't mean for intentionally drawing or going to time in a tournament to work with this, so that might need some clarification in the wording.

Is there any other problem? Mostly this card relies on the sexyness of its wording.

No; the design aim is clear and the functionality is pretty much there.

Punchy wording, to make it only work from symmetric sources... Hmm.

How about:
~ deals 3 damage to all players at the start of your upkeep.
If the game would be a draw due to multiple players taking damage at once, instead; you win.

Actually, I prefer it to be a Johhny open combo with cards like Divine Intervention. It isn't like it's going to happen that often, so you might as well reward creative thinking.

You would deserve a prize for something like that.

Fair enough. It's a bit weird, but what the heck.