I personally think just a much more useful set of exams (i.e about 5x as many exams per student) would be so so advantageous.
1) If you're sitting 50 exams instead of 10, every year, the pressure of exams will go down. Each one means less.
2) Tiny mistakes become less significant. In some exams these days, you can go down a whole grade by a carried forward mistake - which seems outrageous to me.
3) There's too much content we learn that never comes up. Why not test everything - all your doing is adding an element of chance to supposedly representative scores.
This, may I add, would also drastically decrease disparities between exam boards purely due to how much more representative results would be.