[rndgermandude]

>After all, user surveys keep indicating that what Mozilla users want more than anything else is to pay for User generated MDN content.

This isn't what's planned. They will not be charging for user-generated content including all content currently available on MDN. They will be charging for additional in-depth articles as well as some "premium" features when it comes to personalization and easier off-line use[0].

[0] and of course nobody will prevent you from rolling our own such features or even a competing MDN-like site, as the content is available under CC-BY-SA-2.5 on github.