> So all Wikipedia's content added between now and the relicensing resolution (in one month at best) must definitively remains GFDL-only ?
> This clause seems to prevent any effective relicensing (esp. given that almost every important or large article in WP is edited more than once a month).
That clause only applies to content not originally published on a GFDL wiki. In practice, almost all legitimate new Wikipedia content is original to one Wikipedia or another, and most of the rest is public-domain. The only affected content should be incorporation of other GFDL works, like FOLDOC (unless that was already published on a wiki someplace), which will need to be put on hold until the decision is made one way or another.