If those spy shots were from a few years ago, the production model will look drastically different with how much vehicle designs have changed over the years. Also the rivets tells me the body is just a tester and not indicative of what completed XS will look like.
Jaguar seems to have put the XS on the back burner and concentrated on SUV/crossovers or their new Project 8.
Odds are all that will carry over is just the platform used here in this test mule, aside from that its nothing more than an entirely different vehicle wearing the current XF's body. Some companies are very tight lipped and covert about development. I haven't known JLR to be overt. However it comes to market I hope we get enough of what project C-X75 has going on.