Just to clarify a couple of items since I'm the OP. The BMW E9x seats have been crash tested and have passed. The testing was actually completed many months ago.
The Schroth specific application for BMW E9x is tied up in legal issues with licensing and manufacturing as evidently (per Schroth USA) they will be manufacturing or assembling the belts here. As of today (Aug 18th) there still is no official release date.
Now regarding the Mini application, Schroth USA won't comment or recommend the Mini application in our cars due to obvious legal liability issues. However, as noted above by Autobahn335 Mini belts have been fitted to our generation M3 and at least for the E92, do fit and Autobahn335 plans to put them in his car too. Obviously, this would be an "at your own risk" type of application and the mounting points for the outboard connections would have to be confirmed and whether the tail length is sufficient for the E90 as well is still unknown.
Also, and this won't be confidence inspiring, but according to Schroth, the DOT "certification" is just for the fact that the seat belt release is a red button and not really anything regarding it's strength or crash-worthiness.