What a friend from Polar had told me is that the FAA (not sure they can make these decisions) said that they won’t allow a dual certificate operation, where pilots can fly on either certificate. This is apparently due to potential CRM issues. This is just what I have heard from him.
That is BS. It comes from a rumor of a misinterpretation of what one FAA guy is supposed to have said at a check airman meeting last January.