So far I know and understand is that Project E will be Divinity III !

And project D = Dragon Commander and this game will come sooner than Divnity III and DC is a TBS-RTS-RPG genre, fully unique in its sort
The story of DC plays in time line before Divinity II, even before the first Divnity game I believe, correct me if I'm wrong
It's a game one/some of the Larians was just "trying" something and afterwards discovered this "try"(or whatever it was) was a very nice idea and so it grows and become a upcoming new game, certainly & probably (imo) a fantastic fun to play strategy game in which you can play(a roll as it is) your own story !