We have a similar problem in Brandenburg and Mecklenburg, where also a number of small “roads” - usually connecting villages - looks rather like bad forest tracks.
My preference is: highway=track, tracktype=grade1-5, surface=???, motor_vehicle=yes. This way every average map user can see that it not a paved road, but on the other hand it allows unrestricted routing for cars.
But it truly is a difficult topic, and there are also other opinions (highway=unclassified, surface=???). Inventing a new category would be IMHO the worst solution.