School Exchanges by GPA

Maastricht University requires most business and economics students to spend one of their six semesters at another university. Students choose from more than 100 schools covering six continents (no exchanges with Antarctica!). The number of slots available varies across schools; unsurprisingly, some schools are over- and others under-subscribed.
How to solve these problems of shortage and surplus? Simple: the University rations by student GPA, with positions in the queue for each university allocated on the basis of GPA. This year, the greatest excess demand was for Sciences Po in Paris-the three slots were filled by students in the top 20% of their class. Other cases of excess demand this year were Simon Fraser University in British Columbia (post-Olympic publicity?) and, as in every year, the University of California campuses. Is rationing by GPA sensible? To me, it seems both fair and incentive-compatible; it gives students an incentive to perform well here, and the more desirable campuses get the better students. But is there a fairer and more efficient system?