The receiving countries would not accept a regulatory body. The current international regulatory bodies such as the WTO and World Bank are essentially run by the rich countries for the benefit of the rich countries and so they accept it. Any body regulating migrants’ rights would, however, be doing the opposite-- benefiting the poorest -- meaning the rich countries would try to prevent the creation of such an organisation.  In the unlikely event that the regulatory body could be created it would face a gargantuan task. How could global migration be monitored and regulated by an international body when even national bodies in rich countries are not able to keep track of all migrants in their nations? Yet the international body would also have to monitor the conditions of migrants in many much poorer countries where the infrastructure currently does not exist.