I'm thinking they're going to give us back a first gen since it's only going to come with a 90 day warranty.
One of Apple's keys to success has always been inventory management. People here are thinking that they have legions of 6 year-old iPods sitting around? Enough to fulfill this program? No way.
Make new ones? No way. That equipment is long gone and the expense of setting up a new line for so few iPods would be far more than just sending a new version.
So, they're either going to repair the old ones or they're going to replace with current generation. The question is...what costs more - the replacement parts (battery and replacement back) plus labor to send it through the administrative chain and repair it, or the manufacturing cost of a current generation iPod Nano?
I'm going to send mine through the program and I consider it a win either way, but I don't see repair of the old one nor replacement with a previous generation as anywhere near realistic. I'm guessing the replacement will be current generation in a plain brown wrapper -- limits packaging/production costs and the 90 day warranty cuts their warranty risk. It's what they have on hand, gives them a chance to even better manage their inventory of the product (6 week replacement means they have wide latitude to fit it into their production schedule). I'll bet they can send new-generation replacements for $50 a unit or less all-in.