I asked about the reason for the factory shut down while I was going round the Leipzig factory last week. They said the main reason is to redesign the exhaust systems to include a particulate filter for the petrol engines, ahead of new EU legislation next April. Apparently this is a big job for them, hence the shut down and retooling required.
I also asked about other parts of the face lift such as rear lights and removal of switches from the central tunnel. They were a bit more vague about that.