They effectively already do this by selling highly asymmetric connections. They can't do much more than they already are because you have to have enough upload bandwidth to acknowledge all the packets you receive when downloading. And too many customers (and large companies) would complain to Congress if uploading a picture to InstaGram or a clip to YouTube took several minutes or cost a lot of money.
That would impact the ability of users to access corporate VPNs and work from home. My hope is that that's a large enough user base that they can't limit it too much.