People seem to not understand what exploitation means, it falls in line with an aspect of strategy to utilize a weakness or flaw in order to improve your effectiveness in an aspect or goal. Which is exactly what is being done with dark devices. It is not cheating, however it is the abuse of a function or aspect of the fate. And i think they have bigger things to worry about then a single fate's abuse. For one a good majority of the content has already been completed let alone the server and gold seller issues. So unless it falls under the catagory of game breaking exploitation like speed runs - where the unintentional heeling of monsters allowed players to skip content, i don't think it will be on their top to do list for some time.