I came across this picture while looking through some old Road and Tracks, the Sept. 2003 issue specifically. They said it was the 2005 STS, but we now know that's wrong. I wonder if it's a future concept car or maybe a prototype for that ultra luxury sedan. It's definately a continuation of the Sixteen theme. Anyone have any ideas?

I saw that too. I seem to remember the caption saying that it was the upcoming STS, which we now know it isn't. Personally, I think it's a photoshop-job using what may be a Volkswagen or an Audi with Cadillac bits grafted on. This was probably done just after the unveiling of the Sixteen in 2003. I suspect it was done to give an idea of what a production Cadillac might look like based on the showcar. The grill is right off the Sixteen concept, the headlights look like the XLR, and so on. What ever it is, it's a nice design.

Road and track has digitally edited photos *a lot.*

In the photo credit, it probably says something like "photo-illustration by:"

You're right K2K. I looked next to the photo and sure enough it says "Computer enhanced image by Radovan Varicak". So I guess we're never going to see this in production, which is a shame because its pretty nice.