Somebody once told me that everything gets rebooted, and that the window between them shrinks each time.
Despite "ending" just eight years ago, the SHREK franchise will be rebooted for Universal by the creator of the Despicable Me franchise, Chris Meledandri, which sunk in quality pretty damn quickly. Also, this man is working on an animated adpataion of Super Mario Bros.
He wants to revisit the characters but not change the voice cast. So I don't see how this isn't Shrek 5 instead of Shrek 2.1.
Universal owns both Illumination (Despicable Me) and Dreamworks (Shrek).