The issue isn't really living with 500 MB/month of data. For most people, it will simply be knowing that you can do that. The next issue they will face is having the technical ability to actually do so. Then, once you've done all of that, the question will remain: will they be interested in the stripped down Internet. A lot of us who frequent HN may be since the results will still reflect our interests. There are people on IRC who we would want to talk to. There is a slant towards tech sites with RSS. And so on. That isn't going to be reflected in sites targeted at a general audience.
Some of these guys have been locked up for 40 years straight. They're not doing all that extra stuff. They want to go on Indeed or Monster or YouTube. One job site I had to load on my desktop to find out why it wasn't working for them, only to discover the pages had a 250MB payload of random crap downloading, including videos.
But as a practical matter, what people rely on phones for are services that are app-based. Good luck completing a Venmo transaction or any amount of banking.