I like this and had a similar idea. It did not involve "leveles" but a learning tree, extremely similar to the one found at http://www.khanacademy.org/exercisedashboard . So you would not need "character classes" or "levels" but had an immediate view on the persons abilities. Based on the learning tree you can of course introduce "levels" as a branch of the learning tree and calculate "character classes" based on the proportion of the mastered skills.

Ultimately, this amounts to order all human knowledge into a single hierarchy, but can fortunately be performed step by step. Khan Academy is a first attempt at this though aimed at children, not adults.