A user-friendly "Binge On" implementation can be done. You don't need to force plaintext or throttle anything. You just watch traffic at the L3 level, and if it's one of the IP addresses of Spotify or Netflix or whoever, don't record that traffic in your data usage accounting system.

You want Netflix to go faster? Work with them to add a bunch of cache servers with the couple hundred most popular movies, and have your DNS servers point to those. If you want to only do this for 480i video, have Netflix add a small setting that only shows up when you're running on a phone on the T-Mobile network.

No need to artificially slow other video down. You get to make the same marketing claims, except they're true now. You still get to be the "free data for all my video" carrier. Netflix might get a few new users (because mobile is making it feasible for normal people to avoid having computers or land-line internet connections again). Everyone wins.