It is thought that these pictures of the Jaguar test mule is likely to be the XF and the first sighting of it at that. It is due to be ready for the 2016 model year, with the current model being around for five years. It is expected that the test mule is probably assessing performance of the powertrain or chassis components.
The wheelbase looks stretched and the track is wider than the 3 series XS. However it is always possible that it could be a mule for a Jaguar Land Rover vehicle like the Range Rover Grand Evoque or the Jaguar C-X17. It will be a while until it is possible to unpick the images and clarify exactly what it is but it certainly shows that Jaguar is trying to improve something.