Na, that one wouldn't work in practice.
I think you'd be cancelling out a bunch of other quality guys that were brought up through different channels. It is good to be exposed to several different types of aviation-avenues to make you well rounded I supposed, but making CFI/IP time a hard requirement wouldn't work smoothly in practice.
A good way to harder them up is to stick them in the gnarly 135 crazy-town world, among others.
And like someone else said above, the ATP is just a piece of plastic. Not really "proving" a whole lot, in my opinion. My sister could memorize the gleim portion (Ok im exagerating, but you get the point), and a weak pilot could muscle their way through a canned-florida ATP ride in a duchess.
But I cannot argue with making the ATP a req. for operations like 121 FO. Won't absolutely ensure anything at all, but at least a step in the right direction.
But then again, some guy made a good point above, about guys doing thouands of hours of flying only neededing a commercial ticket, then getting the ATP as an add-on with a type, etc. So then you have that situation. So hell, I dunno the answer. Carry on......