Farmers/sellers aren't looking for specific items. All that matters to them is that their box crews can 'mine' Kronos by grinding an easy camp 24/7 and occasionally dropping those ultra rares. Good. Behind the facade of 'I love to see my casual friends getting those raid items' there is always a much simpler mercantile interest. The main problem with those ultra rares was them being attunable. No-trade items could indeed serve the purpose that you have in mind. But anything that can be sold will be abused.