As long as...
1) No "Unlimited" plans, unless it is indeed unlimited and yes, throttling does count, not just a hard cap on data use, since that is the measure they're using to decide who is to be throttled.
2) Give some indication to users where the demarcation line is. Saying 'Top 5%' is fine, but how much is that? I assume it depends on traffic in a given time period on a given cell, but if that changes over time, How does the user know when he/she is reaching that arbitrary line?
3) Seems unfair that a user could use a given amount of bandwidth in one low contention area, but that bandwidth is throttled if he/she moves into an area of high use, solely based on previous usage, rather than a fair contention.
Pfff.... They WILL get away with it, and as has been said many times, the FCC has been castrated by years of telco (and others, to be fair) lobbying.