Keep in mind that the cost of the GRE nearly doubled when it went onto the computer, and I bet plenty of folks are going to have trouble with a $350 MCAT, particularly if they have to take it two or three times.
Also, there will be no opportunity to skip a difficult passage if you routinely don't finish a section in time. There will be no opportunity to go back to a question that you get a sudden insight on, either.
On the GRE, if you do well on an easier question, you get a hard question. If you consistenly do well on a certain type of passage, every question you get is hard, and it slows you down and makes you more likely to run out of time. Can you picture an MCAT like that?
My score on the GRE dropped nearly 100 points when I went from paper to computer - plus I paid nearly double to watch it drop. Let the blessed MCAT stay on paper as long as possible.