You may be interested in the IMS standards which include some work on competencies and storing learner information based on tracking.
http://www.imsproject.org/
Eventually, if/when IMS becomes more widespread, I'll be interested in integrating some of their standards into Moodle if only to gain a level of interoperability with other systems. A side effect might be more support for teachers to offer different teaching with different students, but we'll see how it goes, I suppose.
Implementing things as you've described it sounds like a very big task.
How will it determine student progress?
How does it organise custom quizzes in a fair way? One simpler solution to go some way towards what I think you're saying might be to use "locked" quizzes. That is, you can't do quiz 2 until you've done quiz 1, and you can't do quiz 3 until you've done quiz 2.
From my point of view, a student who "passes" a quiz has not necessarily learned anything useful. Short-term memory is a wonderful thing.