In context: CD Projekt Red (CDPR) has always been a pretty ambitious developer. Simply looking at the escalating quality of the studio's games since it first launched the Witcher 1 provides us with ample evidence of that. The difference between the Witcher 2 and Witcher 3 was massive in terms of scope, and we can expect a similar jump in quality with the inevitable launch of Cyberpunk 2077.
Even with CDPR's bold nature in mind, though, few people truly expected them to deliver on their intent to release not one, but two AAA titles by 2021.
If you have no idea what "intent" we're referring to, we'll start with a little background information: on CDPR's Capital Group investment page, they lay out their strategy for the coming years regarding game releases (among other things).
In the section marked "2017-2021," they've always stated that they plan to launch two AAA titles in that time frame.
Obviously, Cyberpunk 2077 is one of those games, but the other has always been a mystery (and no, it isn't Gwent: Thronebreaker).
Given that 2020 is just around the corner -- comparatively speaking, anyway -- it seemed impossible that another title could be released in such a short time frame; especially since 2077 will likely get the same post-launch DLC and support that The Witcher 3 did.
However, it's clear that the company has some sort of trick up its sleeve, because they've just confirmed on their official forums that their plans have not changed. If you can't read Polish, the English translation is as follows (via ResetEra):
As far as the strategy of the CD PROJEKT Capital Group for 2016-2021 is concerned, its plans to release the second AAA game by 2021 remain unchanged. We are currently focusing on the production and promotion of Cyberpunk, so we do not want to comment on further projects.
Perhaps this second AAA RPG will be an online version of Cyberpunk? Regardless, we wouldn't be surprised if the studio revealed this mystery game at this year's E3; perhaps alongside a release date for Cyberpunk 2077.