I had no doubts that whatever Nano sent would be replace with an equivalent model (i.e., white 4 gig sent, white 4 gig received). Consumer complaints otherwise would cause a media storm. Also, as I said previously, it is likely that Apple is refurbishing as received. I agree that it's unlikely that they would have heaps of refurbished units in stock. There's a six-week expected turnaround, so I have no doubt that this is an estimate for the time needed for refurbishing and shipping received units.
Also, a 90-day warranty is standard for refurbished products. I'm not sure a device this old would be eligible for an extended warranty, but even if so, it wouldn't be worth the cost.
I think some of us are worrying unnecessarily. This recall is just one of the many safety recalls that happen every year and across industries. Look at it as an unexpected surprise! Who knew that such an old device would ever be replaced? If anyone has a qualifying Nano that they don't want to let go of, or are afraid won't be replaced (in spite of the common-sense advice offered here), then keep your Nano. I wouldn't advise it, but if the recall distresses you more than the risk of a possible overheat, then that's up to you ("you" meaning anyone).