I highly doubt by the time the end of the year rolls around, they will grandfather in current unlimited data customers like they have with the Thunderbolt.
They have to, and will. I have already asked multiple Verizon salesmen and customer service reps. The data package is part of your contract. If you sign a two year contract with a $30 a month data package, you are grandfathered into that $30 for those 2 years. After those 2 years, then you have to choose a new data package.
But where they get you is the detail that you are technically upgrading to a new network. They have to provide a $30 data package for 3G, but not 4G. When you want to upgrade to 4G they can grandfather people over (like they did with the Thunderbolt) but they don't contractually have to