Even so, 300GB is a lot of data. I think 1080 HD from Netflix is about 2GB / hour, which means 300GB would be 75 2 hour movies. Even if you watch 3 episodes of your favorite series a night, that still leaves 120 GB of data for everything else you'd do online.
I really don't see how anyone could use 300GB /month, (that's 30GB per DAY). And even if someone could use that much, it's probably less than half of 1% of users.
Maybe UHD will change this, but without that, I don't see how it'd be a problem. It would take a lot of work even to find 30GB of stuff a day to download, not to mention the time it would take. A 10Mpbs download is 1.25MB/s. That's 4.5GB per hour. So you'd have to download at max speed for 6 hours and 40 minutes every day to hit the max. I sure wouldn't get close to that much.