thanks for your answer, and your questions. Very good draw. I printed it in my office ^^

First i'd like to precise that, as in title, aim is not to gurantee quality but minimal quality. I think it's really two different things.

About metrics, my ideas was about following (for the moment):
From your question on objective metrics, i don't think that reliable metrics exists. We can only verify that minimal quality can be reached. As you say, it's a subjective apprehension, but in my mind, this "PEP" could be a guideline to improve development for some developers.