Medicine may not be tying outcomes to licensing/boarding exams like they should (though some studies can easily be found on google scholar), but as I noted earlier, medicine has health database organizations, and psychology just doesn't have that kind of data lying around.
So we can create all kinds of new licensing/boarding tests if we want to, but we haven't even established that they add value. Crappy training programs abound that have APA accreditation, and all of us know horrible practitioners that are licensed. Without data, the next test could just become more of the same. If every new psychologist is going to be required to shell out hundreds of dollars more to get licensed, there should be some kind of demonstration of need and purpose. Boarding is obviously a better solution, but boarding is also voluntary. The phase 2 exam would be a requirement, which creates a moral hazard: The ASPPB has the ability to charge whatever they want and any new psychologist will have to pay it just to get their career started. Because of that moral hazard, there should be a clear demonstration of the need and value of the second exam PRIOR to deciding to implement it. It doesn't seem that this is the case.