After just two single games I've noticed a rather annoying tendency for Sion's passive. As soon as he dies the enemy just steps about 5 feet away, launches any kind of CC in his direction, and he's dead from bleed out before he can even take 3 steps.
1: Shorter or no wind up - This makes it harder for people to simply just walk away from him.
2: His speed booster removes/ignores slows on cast - This way one single slow, possible an AoE not even aimed at him(!), wont render him completely useless.
3: Slower bleed out - Rather than him losing a percent of his HP every second, make him lose a flat amount. That way Sion's extra HP will help him survive longer, rather than just causing him lose even more health every second.