Hi Mark,
Do you mean you think this could be done right now? Or that this feature could be added/developed?
Either way, what more details would you like? (I should have mentioned before that we are currently running moodle 2.8.5.)
Luckily for me, I only need to provide the technical solution - faculties, departments, and individual professors make the decision about whether they can or should change individual student assessments weightings in their courses. I expect that most of these cases occur when the final covers the same material as the midterm...
Thanks,
Dave