If the CAA can delegate the task of examining an individuals ability to fly, surely they can delegate the task of checking the paperwork, to ensure it is in order.
As a point of interest, how many applications for a PPL are turned down each year. By this I mean turned down, not returned to the applicant because of an error and then issued once the error is corrected.
Whether one agrees with the idea of a temp cert or not, the only ramification would be that a newbie, having passed the skills test, could be flying around with pax for a few weeks before their application was disallowed as a result of a discrepancy in the paperwork. Against that is the fact of 2,500 new PPL's, each year, generally sitting on the ground losing currency ahead of their first proper flight as PIC.
As discussed here recently, many people never make a flight as PIC with pax. Some because by the time their licence arrives they have lost the confidence they had at the time of the skills test, and they are out of the flying club habit.