It's a Wiesmann GT prototype. They have been hinting at developing one with the V10 for a while. Currently it uses the V8 from the 550i. The car weighs ~2600 lbs, so you can imagine how fast it must be with the M5 engine.
I wonder how fast it was going when it crashed? The pasenger cage appears to have survived admirably. The rest of the body is fiberglass.