I question how much “information” is contained in dirtbike:scale=?. Something like: “the difficulty of this trail for dirt bikes is somewhere between the most easy and the most difficult, but I am not sure because I haven’t seen the trail, because if I had, I would have a more precise value. I just really want it to show up in the app I am using”? From what I have seen this tag is being applied over wide geographic areas in single changesets (indicating most likely no on the ground survey) to any trail that is legally open to motorcycles. If the trail had been surveyed, the mapper should have a better idea of the dirtbike:scale. Thus, the “information” that is being “lost” is de facto embedded in the motorcycle tag as the mapper is most likely guessing that any trail where motorcycles are legally allowed must also be suitable for dirtbikes.
How is it that a mapper can know that a trail is suitable for dirtbikes, but not have some idea as to the level of difficulty?
If you find a trail that is legally open to motorcycles, but is not suitable for dirtbikes, tag that trail dirtbike:scale=6 (which the wiki says means “entirely impassable for dirt bikers”). Then data users/consumers can just assume that in the absence of dirtbike:scale that the trail is somewhere between 0-5, since it appears that those mappers applying the tag dirtbike:scale=? are making that assumption.