Interesting concept, but I see more cons than pros, at the moment.
Where I live, AT&T has pretty much monopolized the area(countryside). A few months back, they upgraded my service to an unlimited data plan, but I have my doubts.
I'm using the 'fastest' plan they have available in the area. I guess the speed is ok, considering where I live, but what they're charging per month for it is absurd.
~$70 a month for just 18Mbps...
I do agree that something needs to change with the ISPs, or many won't be able to use/afford Stadia, especially since most gamers are on a tight budget anyways.