I theorycraft. I theorycraft a LOT. I mostly design custom changes to items, refraining from touching champion balance or other stuff. Sometimes I'm spot on. Most of the times I'm wrong. All in all, I like doing it - when I come up with something that later appears in the patch notes, it's just a bonus.
I play on the EUNE server under the name Pyro.
Pyro's Item Overhaul
You can find the complete overhaul here. Or you can simply click "show" to expand the whole item list here.