What if Sion could ult after he died?

I just was thinking of ways to make Sion more thematically awesome (even if he's already up there), and since Riot has been giving him small nerf after small nerf, I was thinking of a decent way to buff him, without breaking the guy.

So, if his ult's not on CD when he dies (say he's being chased and slowed and can't get away), wouldn't it be kinda cool if he could turn around and kamikaze into the enemy team for a counter-engage? Karthus-esque?

I think his passive's a bit lackluster, especially because all he needs is a single slow to fuck up his chances of revenge-killing anyone. He'd still lose health during his ult charge, and can still be damaged, but he'd retain his CC immunity. Because obviously we know he can run around and punch people, so charging shouldn't be that hard to imagine.

Thoughts?