A bit of mostly useless math:
D:OS released on June 30, 2014.
D:OS2, which is obviously great, but still quite derivative in many aspects, released on September 14, 2017.
That's 1172 days for an iterative sequel.
Going 1172 days forward from D:OS2 we'd reach November 29, 2020.
But it seems pretty likely it would take them longer to do a BG game than a direct sequel.
(Also, the gap from Divinity 2 to D:OS was 1683 days, but they also made Dragon Commander in between)
D:OS released on June 30, 2014.
D:OS2, which is obviously great, but still quite derivative in many aspects, released on September 14, 2017.
That's 1172 days for an iterative sequel.
Going 1172 days forward from D:OS2 we'd reach November 29, 2020.
But it seems pretty likely it would take them longer to do a BG game than a direct sequel.
(Also, the gap from Divinity 2 to D:OS was 1683 days, but they also made Dragon Commander in between)