I joined PM long after the new plans were introduced, so this doesnt apply to me.
I saw @annemarie post on this topic. For several years of customer loyalty, it would be reasonable to get a loyalty reward and feel included regardless of the plan you are on.
It doesn't have to be a discount on the bill. Perhaps a data add-on or some other perks PM can come up with.. this will get customers on the grandfathered no-data plans to try out the amazing 4g/LTE data, for example. It may lead to the customers upgrading their plans in future.