Another reason for not having this is if we did, I assume there would be levels like the current academy, along with tags to identify the level reached.
All this will do is give tags to the extremely talented/popular moc builders and then others who may have different tastes might never get up through the ranks, but they like the way they moc.
AS I said before moc'ing is more personal than reviewing because it's your interpretation, not a pre defined set. It's really hard to create a system of different levels to achieve when there can't be a set standard for each level.
It works with the reviewers academy because everyone can be trained to do a good review and you can't alter the set in a review so it makes a more even playing field.
Again, a good idea on paper but much harder to implement.