It turns out that GSC Game World's announcement of Stalker 2 has been nothing but a ploy to attract publishers at E3, since the game itself is still in the early design process. Interestingly, this was revealed by Epic's Sergey Galyonkin.
Galyonkin was speaking to the crew behind the Russian podcast How To Make Games, where he revealed how exactly he knew about this. It turns out that Epic Games are licensing their Unreal Engine for Stalker 2, although it's obviously barely been used as of yet.
He also spilled the beans on GSC Game World's roster and the team behind Stalker 2 is not the same one that did Cossacks 3. Several members form the original Stalker development team are there though, which should ensure the sequel doesn't stray much from the original idea.
This explains why the recent had nothing to show for it other than "Stalker 2021" on a black background. Obviously, the team haven't really got anything down yet, which doesn't seem like a particularly wise strategy.
Of course, I could be wrong and GSC Game World could successfully reel in a big name publisher at E3 2018, although I suspect a very low likelihood of that happening. After all, getting a serious publisher in the industry cannot be done by hype alone - you better have something to show for it.
GSC Game World's earlier attempt at the release of Stalker 2 was a mess as well, which surely can't help their case with potential suitors. The company had started working on it in 2010, supposedly sculpting Stalker 2 on their proprietary engine, although those dreams never came true.
Stalker 2 was cancelled, then confirmed, only to be cancelled again, somewhere around the date it was supposed to launch. Ultimately, most of the team moved on to work on Survarium, albeit under the flag of Vostok Games.
GSC Game World
All things considered, you may not want to get too hyped up over Stalker 2, because it may just as easy turn out to be a ringer. It wouldn't be the first time.