With ISPs (at least in the US) moving towards data caps, this is becoming a reality. It won't fix the problem.
DDOS attacks via IOT don't have to send much data per request. If my devices are doing an extra 10Mb/hour, I won't notice. 1000 homes is 10Gb/hour and that's just a few blocks in a city. 100,000 homes seems easy to hit, which is a petabyte of data per hour.
It's death by a thousand paper cuts. If my internet bill goes up a dollar per month, it's highly unlikely I'm going to debug my refrigerator to figure out how to stop it.