There's not too much that can be seen in these photos, as the mule uses a modified current-gen body. But the car definitely looks like it has a wider track, which could point to the next G being a bit larger (or at least meaning it's not going to shrink). We can also see two extra air intakes in the front bumper, just under the grille.
The photographers tell us that the cars were snapped near a Mercedes-Benz test facility in Northern Sweden, leading us to assume that a diesel G is likely to be powered by an engine developed out of the Daimler-Renault-Nissan partnership that was announced two years ago.
Check out all the high-res spy shots in our gallery.