There is a grey area that concerns me though, which is the period between when you request the pre-ordered device and when it actually comes in and ships. According to the droid-life article you are referring to "they" spoke to an unnamed Verizon "PR rep" who said if you pre-order you get to keep your unlimited data. But they weren't specifically talking in reference to the scenario I am referring to.
To put that statement in context, the question was raised as it was referring to the mouse type on the preorder page at VZW that says you can get it for $199 "on a two year contract renewal and that that price requires a data pak with 2Gb of data"
According to the VZW customer service rep I spoke to yesterday, he said when you call to pre-order there is no contractual obligation on either end. You simply get your name in the queue for one. When it actually comes in and ships is when you get billed, or you choose to not accept the terms as they are on the day they attempt to bill it. VZW's entire system works around transaction dates. You can walk in a store and they can tell you anything but what is on the receipt you sign is what you agree to. What they said be damned. Same goes for phone/internet transactions.
So the grey area is between 6-6-12 and the assumed ship date of 6-21-12. According to the rep I spoke to, although highly unlikely, if you pre-order and say on 6-18-12 they launch shared data and do impose the "no grandfathered data on subsidized devices" policy, then that will be the contract terms you will have to accept on 6-21-12 if you still want the device for $199 on a two year renewal.
I find his explanation much more accurate from personal experience. The unnamed PR rep in the droid-life article was probably speaking out of pocket (they are PR after all) and they were also referring to a somewhat different scenario.
I (like a lot of people, probably) would REALLY like to confirm the last part of your post. If you get the terms of when you pre-order, I'm going to pre-order the GSIII now. If you go by the terms of when the phone is shipped, I'm worried that if I pre-order now, then Verizon will implement the killing of grandfathered unlimited data, then I'll be screwed.
I talked with a Verizon Rep today and he said they got new spec sheets in for the S3 that they did not have till late yesterday. The 32GB model is all onboard so he helped me to cancel my 16GB preorder and set up my 32GB order. He also informed me that the onboard slot will have cards up to 64GB like the S2. This is the Verizon medels and may not be true for all Carriers. Some sites were saying micro slot would only handle 32GB. I still have my same unlimited data plan and its stated on the order confirmation.
So they put on the plan that you are guaranteed to keep your unlimited, even if Verizon implements that policy in the interim?
Also, when you pre-order, do you have to pay for the device in full at the time of order? Pay when you get the device? Or can you add it to your bill?