I did not propose to remove it, I proposed to rename it to “free from obstacles”. In this way it is clear that it refers to the difficulty of hiking on it, not to any visual aspect of the trail. The hiking value would then mean that there are no obstacles on the path, so there is no risk of straining your ankle on an obstacle and you don’t need to wear hiking shoes to prevent that. If there are such obstacles, you’d better wear high hiking shoes and the trail should be tagged mountain_hiking.
(from the discussion in German) Our scale was originally based on the SAC scale, but this is no longer the case so we are free to do what we like with it in OSM no matter what SAC is doing in the meantime.
To avoid any more confusion, it may be a good idea to rename the key from sac_scale to hiking_difficulty to make that clear. The key sac_scale could then be redefined and used to tag trails with their hiking difficulty as determined by the SAC (making it 100% verifiable). It would probably only be applied to trails in Switzerland.