The majority of the English gentoo documents that resided in www.gentoo.org/doc/en have now been moved to the Gentoo Wiki. All those documents have been made available in the main namespace, meaning that non-developers can continue to contribute on those articles and guides, fully in the spirit of a wiki and community.
We are now working on a method for displaying an overview of documents that have been moved, or have seen enough development on the wiki that they are deemed of proper quality and stable (not too many changes left). Currently, such documents are (requested to be) marked for translation, allowing me or other developers to review if the guides are indeed ok to move forward. If so, they are marked as translatable (allowing the various translation members on the wiki to move forward with translating the guides) and will be made part of the overview as well.
One of the few documents that has not been moved yet is the Gentoo Handbook as it is of a different format than the guides, and includes dynamic documentation generation features which I have yet to fully investigate (wiki-wise). I currently focused mainly on the non-handbook guides, so the handbook itself will get more attention later (after the documentation overview is completed).
Big thanks to Alex Legler for assisting me and providing the necessary features and functionality in the Gentoo wiki to make this all possible.
Edit: added link to overview page.