Blitzcrank's speed slow won't work out, but I like the idea.

Not many champions have a disabling ability after casting a spell. In fact, I don't think any other champions have a direct negative effect after a spellcast. The closest I can think of is Rumble, gnar, or evelynn's passives. I certainly like the idea of something like this; you have a negative effect to worry about if you screw up your timing. The problem with it is threefold:

1. the speed bonus doesn't last long enough to be worth the slow, making blitz an ineffective champion right now. I was talking to my math wiz friend about this, and he was saying that since his speed decays exponentially, the boost only raises your speed effectively for a moment, before becoming "not worth it" for the majority of the time.

2. No (most, as I said) champions don't have effects like this.

3. the game's state doesn't support a "give and take" mentality like this yet.