After reading many articles about the pros and cons of the world of folksonomy with tags and the world of taxonomies with ontologies and classification, I am not quite sure how it will fit together. The dashed line in the center of the pic marks the frontier. At the moment I do not believe in reassambling, but maybe there will be something that pushes it forward.

Hm well, I think they necessarily don’t have to fit together 1:1. For me it’s two different approaches: Taxonomy is top down, Folksonomy is bottom up!
Folksonomy has the intances (data) and needs classes, Ontology has the classes and needs instances. In case of a good ontology they may meet in between, but yeah – this is the trick!
Recommendation systems which offers classes of the ontology to tag may bring them both together!?
Here is an other answer. To suit the whole thing together you’ll have to build up an ontology by using tagging and make some asserstions: The TagOntology
[...] at the following drawing. Some weeks ago i thought about how to connect the tags with some order. Slowly it gets clearer. One have to use existing classifiations. My first try will use wikipedia [...]