What Lacrymas said.
And besides:
Divinity: Original Sin is their most successfull game and if everything goes right, they will earn even more money with
D:OS 2, so it would be stupid at least to think about another game like them. Besides the gameplay of
D:OS fits their dream of a big world to explore most.
For repeating the formula: Well, the Timeperiod of
Divinity 2 is another, than the Timeperiod of
Beyond Divinity. They use Airships now. And we had some Steampunk elements. So they could freshen it up a bit with some machines and guns for the grand finale?
And after that, I don't know. Another
Dragon Commander? A new Action-RPG-IP? Wouldn't be that bad

.
Personally, I would love to see another
Dragon Knight - Saga, with every gameplayelement fixed.