I have no problem with encouraging additional tags, and I often add many of these tags myself. But…
The devil is in the detail here. Which descriptive tags exactly? Of all possible tags mentioned in this and previous posts, only “surface” seems to me relatively unproblematic (provided we accept=paved and =unpaved as generic fallbacks).
Smoothness: defined for wheeled vehicles, which will be irrelevant for many paths, and even where it is relevant, should we force mappers who walk a trail to also consider conditions for wheeled vehicles at every point in a trail?
Width: often varies widely over short distances for “unbuilt” trails making it very time-consuming to survey and map. Sometimes hard to know where the edges of a path are, e.g. over grass or sand (and in those examples they often don’t matter much anyway).
Sac_scale: defined specifically for hiking, no appropriate value for many “easy”
paths.
Trail_visibility: defined for hiking trails, sometimes difficult to interpret (e.g. if the trail itself is worn away but markings are easy to follow).
Informal: often difficult to determine, and can’t really be validated unless we also force mappers to add formal=yes.
… and none of those even start to cover access.
So there is a danger that we are defining millions of objects as “invalidly mapped” where the solution requires a lot of survey, thought, and interpretation on the part of mappers. Constantly nagging mappers who improve the map in one way (e.g. correcting the position of a path) to improve it in other difficult and time-consuming ways seems to be going too far.
So in general mappers of ways for non-motorised transport have to tag 4 or 5 things at a time.
Meanwhile, mappers working on minor roads used or designed for 4-wheel motor vehicles get to choose between residential, living_street, track, service, busway, unclassified, pedestrian etc as top-level tags without being told their mapping is invalid. Or would you suggest similar treatment for those?