A weird kind of Sion buff.
Bare with me for a second. What if, every point Sion put into his Q, the time needed to ramp up was reduced slightly? Say it takes 2 seconds for him to get the full stun (It does). Level 1 - 2 seconds Level 2 - 1.8 seconds etc.
"But hold on!" you say. "Won't Sion be able to spam it at level 5 because of how short the cooldown is?" You're right little Timmy, he would be able to do that. And that might be a little too much for him. This leaves riot some room. If this makes him too powerful, they could nerf it slightly. Level 1 - 2 seconds Level 2 - 1.9 seconds Level 3 - 1.8 seconds etc
With a 6 second cooldown at max rank, and 40% cooldown reduction, that would be quite the crowd control. So what if, instead of his Q decreasing in cooldown from 10/9/8/7/6, we reversed it? 6/7/8/9/10 seconds.
Why, you may ask? Well, if you decide to be one of those players who only places one point into it, you would get to use it more often in lane. This would require you to watch your mana a little more, however. This would also allow you to use it for slows late-game if it's the last thing you level. If you feel that you're skilled enough with Sion to land it at level 1, this would be a good option for you. Howeverrrr, if you max it first, you'd use it less often, but you'd be so much more likely to land the stun. Not to mention, once you hit 40% CDR it would be on a 6 second cooldown anyway, returning it to its original 6 seconds.
Personally, I think this is a neat idea. It gives him choices for laning, and it certainly gives him something to DO late-game.
Thoughts?