Won't work. Hard to compensate people properly who have overenchant sub-85 stuff, because the market usually determines how much that is worth, not crystals, or recipe ingredients, or NPC sellback value. If they try to pay someone who has for example a +30 low grade weapon, or wea with a rare SA, they are likely going to give the owner far less than what owner feels that item is worth. They could do it, but it might leave lots of people unhappy.
Having said that, I agree that all of the NPC shops should be updated with weapons, armor and accessories from S - R grade. Anything below S should be removed from database and archived. It means sacrificing the ability to use Modify Armor and Weapon scrolls to get low level skins, but so be it.