The game was announced back in 2013 but there is really nothing much we know about the game. The trailer does reveal that the game will be set in the far future and that CD Projekt Red has every intention to make it much bigger than the Witcher 3 but that is all we know right now.
Earlier this year, there was speculations that the game would be release later this year but looking at how little details we have right now, we think that that is highly unlikely. Then there was talk about the game getting delayed after it was reported that CD Projekt Red is doing an engine upgrade.
However, CD Projekt Red has come out to clarify that the engine upgrade will not affect the progress of the game at all. Most people predict that the game might arrive in 2019 but we think it might be earlier than that.