Potential fix for Sion passive?

Hey Riot, I think we can agree that new passive is really, really weak. And I mean, he has a good kit outside of that, but you literally can't do ANYTHING with his passive. One slow completely negates it. I don't want it to be too strong, but it's just the most pointless thing right now, and as a result feels really lame thematically.

Is there any chance you could make it immune to soft CC, kind of like a Master Yi ult? I feel like that would really shore it up and make it feel a little more meaningful.

Just a thought.