Though I did not explicitly mention it, it is only logical that if a big chunk of tuition were to be required at the time, financial aid would have to become available at the same time as well. All I'm saying is that it would force a lot of those individuals who are likely to drop right before classes start (or when tuition is due) or drop in general at an earlier date. Yes, it could be problematic for med schools in that it could result in unfilled spots, but I think the problem would be minimized with the $ commitment. That could be solved by a smaller, more realistic waitlist where applicants are informed of their chances.
Here's another crazy idea: Since most (all?) med schools have started classes by August, why not open AMCAS submissions in August?