They grant the organisation (in this case a for-profit) the exclusive right to redistribute the project (and contributions made to it) under a different license

They grant the organisation (in this case a for-profit) the exclusive right to redistribute the project (and contributions made to it) under a different license. Including a proprietary licence. It is only required if you intend to move to an open-core model, or intend to eventually make the project non-open-source entirely. This is a common first step for many organisations that have moved in this direction. The announcement even makes it clear that they intend to ship versions for a fee, so it's very likely that we'll see a "community edition" and a "full edition" at some point. Or some other model which amounts to the same general idea.