Maybe we could, in addition to the highway=possibly_dangerous_path proposed here for hiking trails, create another temporary highway=mtb_trail for cycleways that a mapper considers suitable for mtb only but isn’t able to add an mtb_scale tag to. This should be understood to imply fixme=I think this is suitable for mtb only, not for average bicycles, but I'm not able to assign an mtb_scale value to it so could an experienced mtb-using mapper survey this path and add it asap. I.e I agree with @Richard , as long as these new highway types are considered to be temporary, to be replaced asap by highway=path + secondary tags describing the quality of the path.