I got an e-mail back from someone at SkyMiles/DL who is a "Specialist, SkyMiles Servicing" before Christmas, after the museum forwarded on my e-mail. Which is far better than I got by e-mailing the general customer service people a couple of times a few years back! Here's what she said:
Dear Mr. Smith,
Thank you for reaching out regarding historical SkyMiles data. I received your note, and I am responding on behalf of the Delta SkyMiles team.
Unfortunately, the information you are asking for is not something we provide. Can you please clarify the reason for this request?
I was confused by the comment that it wasn't something they provide. I didn't know whether that meant they didn't have it, or that they had it but wouldn't provide it, for some reason. I sent her a detailed note back, explaining my avgeekiness, mentioning some FTers had heard it was possible to obtain this information (but not succeeded in doing so), and so on. I indicated I would be happy to pay for the information (as, probably, would others), and mentioned that I had seen somewhere that AA can supposedly pull this information.
I haven't heard anything back since then, unfortunately. If I ever do, I'll be sure to post an update.