Agree.I've been betting on 2019 for years now, and that's not changing. Like @sv3672 said, the game could be farther along than we've thought so far.
As for specific quarters... Q3 seems the most likely, followed by Q4, then Q2, and then Q1. Q3 because it's around the time their past games have released (IIRC), Q4 because they could avoid broketober and the mid-year game rush by launching in December or November, and Q2 because if they're going to release in the first half of 2019, I doubt it'll be the first quarter. Q1 seems like an impossibility to me - too soon. But possible, I guess.
Given even a conservative estimate and saying this game entered production after Blood and Wine, 2020 would mark four years of full production. Thought would be extremely expensive and highly unlikely.
The fact we're even seeing the game as a playable vertical slice means we're fairly close.