In my head the question is: can a wikipedia-style MDN exist? If the answer is yes than I think op opinion is only on one type of model of organizing and funding a documentation site.
Will a wikipedia-style MDN be successful if there are (in addition of volunteers) paid writers who cover the majority of the work need? Maybe not. Maybe that's what the existing MDN proves.
If we go wiki style, can we bootstrap with MDN? Is there a download with an acceptable license that could be used? I don't know if we'd get traction to bootstrap from nothing...
EDIT: So I've found answers to my content questions at [1] - does the community have the appetite for an alternate site?
Will a wikipedia-style MDN be successful if there are (in addition of volunteers) paid writers who cover the majority of the work need? Maybe not. Maybe that's what the existing MDN proves.