Just a few observations:
1.) Now that the e9x is coming near the end of its life cycle, it would the usual time for BMW to bring out a CSL version.
2.) To me, it appears that it is a 'works' version because of 4 things:
2.1) The exhaust is stock. If it were a tuner or even a private car, surely if they're testing/modding it to the extent that they've stuck on that fugly wing, they surely would have gone for an aftermarket/custom exhaust.
2.2) The stick at the front. I am guessing that this is to measure roll angle. I know there are great tuners out there who do their jobs but this is someone who's SERIOUS about finding out how the chassis behaves.
2.3) The antenna on the trunk lid. Whoever is developing this car has the resources/need for one of these. This is an addition to the oem one on the roof. In the photo shots, it was a kind of straight antenna. In the video, it is clearly a slightly smaller version of what is on the roof. I'd guess that only a big outfit would have the resources to do this sort of thing in such a short time. (Assuming it is the same car).
2.4) Lack of any identifiable marks. If they're a German tuning company, wouldn't they have their stickers on it all over the place? Surely we'd see Harmann wheels or AC Schnitzer rear wing or something? If it were a racing team, surely a closed track would be the preferred venue for testing?
3.) All photos of test mules from BMW have blacked out badges (as pointed out earlier). Also, the tradition for CSL models is a light weight version of the 'normal' M3. I assume this would mean CF panels and so on. I don't see any on this car.
4.) There are posts on the photo thread that this car exists (at BMW and built by BMW) and I truly believe that. However, why would they build a (track) car that they don't/won't sell? The next 3 series will have a different chassis to this one, so why bother? Surely their race car development programme tests on the track and would be a lot more different to the stock version than this? Why does this car exist at all? (I still assume that it's just one car.)
The only answer I could _guess_ for my last question is that this was a test mule for the M3 CSL that got killed off about 9 months ago. If they're driving it around now... may be the CSL is back on....?