You sure this wasn't simply confusion with the new Infinity? With the exception of the plastic strip, they look very similar to the existing primes, and any rumor originating at a Best Buy is suspect, and at best, likely to be partially wrong.
I doubt the existence of a modified prime release alongside the upcoming releases, so probably no direct swapping like you've described, but I've been wondering if the big news might be some sort of voluntary trade up program for prime owners to the Infinity. Something like, for those who want the upgrade, send in your existing prime, plus the $100 for the price difference, and they send you the comparable model in the same color back. Thinking it's unlikely, but it would be a great way to reward the early adopters who might now be wishing they had waited.
Barring that, the thing I would most like to see, would be Ubuntu for Android coming to the Prime, and presumably included in the Infinity. It's such an obvious fit for the transformer line of tablets, that it's hard to imagine they aren't looking into it.