Dying Light 2 is going to be a rather substantial release, but the idea that only 50% of the game will be accessible in a single playthrough is quite impressive and somewhat strange still. However, the developers, Techland, aim to bank on this in full.
In a recent interview, Techland explained that they felt it was odd that the first game's gameplay was such an open sandbox, while its narrative was so linear. "The dream with this game is that we could give you the same amount of freedom in the narrative as we have in the gameplay," they said.
In Dying Light 2, "(players) can climb to the top of the highest building, look around and go: 'Wow, I made this'," according to developers. Due to the fact that virtually every facet of the game world is as malleable and reactive to player behaviour as it is, Techland says that a single playthrough won't let you see more than half of Dying Light 2's total content.
It's also interesting that Techland actually tested out some gameplay ideas for Dying Light 2 by introducing small post-launch DLC to the first game: "If we had an idea we're unsure about for Dying Light 2, we could mimic that idea to some extent in support of the first game and see how it works." That way, they could figure out what is that players wanted more of, and ditch what didn't pan out.
In practice, this might mean that some of Dying Light's crazier time-limited events (hyper-kicks, for example) might make their way to Dying Light 2 to some extent. Only time will tell, of course. On a related tangent, is it any wonder we feel the original is one of the best horror games ever made?