According to this kickstarter project, Germany has approved the hitch for they Model S.
Unfortunately, it is only valid for Model S in Germany.
Looking at the work done, it seems to be a decent test, but does not take into account this being an electrical car in any way. It tests the handling and structural strength.
But the price was relatively low and now I can't help to wonder why every Model S could not be approved to have a hitch, seeing as cost doesn't seem to be a big issue.
Anyway, feels really should certify every Model S to be hitch capable. No reason why every country should have to do this on their own, if even possible.