Why to send? Go to USPS with your certificate, apply for ID card & show certificate and then you take it back.
I think there is still some details to be ironed out on how this is going to work. I had to drop something at the post office this morning so I took the opportunity to ask a few questions about the passport card:
The post office employee knew about the card, but didn't know much about the corner cases. She was nice enough to go and call someone (Passport Agency, another postal worker?) to ask the questions. The question that prompted her to make the call is that I told her that according to the site one only needs to pay $20 if already in possession of a passport book. However, she told me I would have to mail the application myself and send the passport book along so if I was planning to take a trip soon that wouldn't be a good idea. She pointed out at March or April for the issuance of the cards.
At first she had told me to provide the naturalization certificate or birth certificate if I was applying for the first time.
I don't think one can apply without sending along proof of citizenship. Have you tried thrix? Were you able to just show the certificate and take it back?
One way or another, I don't see the purpose of sending either the passport or the naturalization certificate for an indeterminate amount of time. I'll wait until they start issuing the passport cards and see what the timeline is. That's in the case that I end up applying for the card.
My 2 cents.