The problem is that the grandfathered plans are protected by law, at least in California and it may be a nationwide thing.I was thinking the same exact thing when I first saw headline....
Basically they are not allowed to change your plan without your express permission.
Verizon got around this by saying the terms of an upgrade is that you are giving your permission to change the plan. But that took until it was time to upgrade your phone before that occurred.
If we were to lose unlimited data here, we would simply take our 30 or so business lines to T-Mobile that offers unlimited data with a high speed cap. The difference there is T-Mobile only slows you down one data level, so if you normally get 4G LTE at a specific location, it goes to 4G, if it would normally be 4G, it drops to 3G, etc.