According to our spy photographer, the reason may be that the car was too loud. He says that the Vettel could have exceeded the 100 dB limit in place during industry test sessions, and that adding lengths of pipe to the exhaust can bring the sound down. This seems like a reasonable explanation, but it also raises the question of why it would be necessary now. After all, we've never seen this setup before.
We have a theory. Corvettes have had adaptive exhaust for a long time now. Perhaps this is an evolution of it. For street driving, there may be baffles in place to keep the exhaust from attracting the attention of law enforcement and deafening the driver. Then, when the car is taken to the track, the driver could flip a switch, open up the baffles, and have a less-restrictive exhaust to get every last pony possible. It sounds like an easy idea to implement, and would certainly attract attention. Ideally, this hypothetical exhaust system would allow for some adjustment, since some tracks still have noise restrictions.
Aside from the strange exhaust, these photos provide another look at the massive air intake vents, front splitter, and rear wing. You can check out the last Nurburgring photos we posted, here, and everything else we know about the ZR1, here.