CD Projekt's big thing right now is Cyberpunk 2077, but in case you'd forgotten, it's working on another major RPG too. And even though we have no idea what that second game is at this point, it's actually scheduled to be out pretty soon: The company said in a recent forum post that the plan is to have it (and Cyberpunk) released by 2021.
The original post is in Polish, and so the standard Google translation mangling applies, but this is what it says after we run it through the machine: "As for the strategy of the CD Projekt Capital Group for the years 2016-2021, its plans for the release of the second AAA game until 2021 remain unchanged. We are currently focusing on the production and promotion of Cyberpunk, so we do not want to comment on further projects."
That strategy was laid down three years ago, in a very vague breakdown of the four-year period between 2017 and 2021: The document says that CD Projekt will, among other things, release Cyberpunk 2077 and "another AAA RPG title" in that time frame. Cyberpunk is obviously the eye-grabber here, since we've actually laid eyes on it, but I think the fact that the unannounced game remains on track is the more interesting part of all this because CD Projekt has remained preternaturally silent about it for longer than most of us probably realize.
2021 really isn't all that terribly distant, especially when you consider that Cyberpunk 2077 was first announced seven years ago, and it might seem unlikely that CD Projekt could take this long to make Cyberpunk and then punch out another big-time RPG in such a relatively tiny timeframe. But the reference in the strategy doc suggests that the wheels have been turning on this mystery game for a number of years as well: Not at the same scale as Cyberpunk 2077, presumably, but enough for the studio to remain committed to the timeframe.
Obviously all of this leaves open the possibility that Cyberpunk could be out this year, or in 2020, or 2021—the great thing about being in the first half of four-year plans is that you've got a lot of room to wiggle—but it's likely still a good way out: CD Projekt warned earlier this month that even though development is well along, "work on it is far from over."
As for the unrevealed project, I've emailed CD Projekt to confirm that it's the one it talked about back in 2016, and I'll update if I receive a reply.