Even adding class percentiles to transcripts doesn't give a complete picture.
Because some universities admit mostly students with ACT/SAT scores in the 90th percentile or above, having a grading scale where an A = top 25% of class can mean something completely different than, say, a grading scale at a different university that admits high schoolers who aren't as skilled at taking tests where an A = top 10% of class. I take issue when people hold Harvard up as an example of grade inflation while my sister goes to a really bad public college alongside students who, based on admissions stats from both schools, did not score at all similarly on the ACT/SAT (average admitted high school senior has below a 50th percentile score) and there is a possibility of 10 to 20 extra credit points on every Chemistry test (tests which, in this particular case, I know because I've seen them are already easier than normal)...yet her school does not have a "grade inflation" problem because there are masses of students who probably shouldn't even be in college who are pulling the average down by a very large amount. Percentiles are simply meaningless in comparing grades at those schools. The Harvard administration has argued for years that their classes are just as hard as any other school, but that because their admission standards are so high, most students perform very well in the classes. It's not possible to try and make a claim along the lines that a 25th percentile (or 50th percentile) Harvard student wouldn't make the top 10% of my sister's class (and therefore shouldn't get an A), although it isn't possible to claim that they would, either.
So I don't think adding percentiles will make it GPA very much more meaningful for graduate and professional school applications. Students just can't be compared like that, which is why no matter what GPA will only remain one out of many areas in which pre-medical students are judged.
