I thought about it, and AS on-hit builds largely don't really scale based on steroids or anything else (unlike AD builds). Thresh, however, infinately scales with AS and his Q. Thresh also gets tanky for free from his passive. So I mixed these two sort of independent stat areas, and the result is this. I think it's pretty good :P
I don't think riot wnats ppl playing thresh like this, so his Q is probably going to get changed, I suspect.
If anyone has any questions feel free to ask. I am streaming atm, so I can't get back to you immediately, but I'll check this thread later.