FWIW, a service advisor at the BMW dealership told me that BMW traced the failure back to an improper material usage by the company who supplied the discrepant stampings to BMW. They were also able to determine what cars those parts made it on to, so there is a certain range of VIN numbers affected by this problem. We could of course disprove this by taking a tally of the production dates of cars affected, as well as the serial numbers.
I was under the impression that OEMs stamp, weld, construct, etc. the entire unibody and don't sub-out those components. I guess BMW does things a bit different.
And the guy above is right, it isn't at all a "subframe" failure. It wouldn't be that big of a deal if it were a subframe issue. Instead, it's an issue with the unibody, the "part" that everything on the car bolts to. Not very easy to re-and-re...