It has not been confirmed that Project E is Divinity 3, though so far what we know fits that assumption.
I also thought of Damian and Ygerna seeing the concept art, at least partly because there aren't really any other couples involved in the story so far. If it is them, rather than some new ominous-looking couple, the game could be set between Divine Divinity and Beyond Divinity. Damian was 15 when Ygerna was executed, though, and they had only known each other for a couple weeks, so that isn't a lot of time to fit in an RPG (which would need to avoid effecting the established story line). If set after DKS, there would have to be an explanation for Damian (presumably) being able to resurrect Ygerna when he was unable to do so before (maybe because the dragon knight's resurrection and re-killing broke the soul forge, or something). It could be set before DKS, so Ygerna was a ghost, but would have to end with her stuck in the Hall of Echoes and unable to communicate with Damian. Other than aspects of the ending already being establish, there would be lots of flexibility in the world and story before DKS to set another RPG.
We know you will be able to defeat the main bad guy at the end of Project E, so that limits the plot if the game is set before DKS (the bad guy has to be someone other than Damian, or you play as Damian, and the 'bad guy' is the Divine One).
