Unless they've majorly rebuilt the thing, idtech5 has major issues with large surface areas, so they would have to make Dishonored 2 notably less open than even the first game.
Now, that's fine if you're making a corridor shooter, but bad if you're not.
I feel it would be unfortunate if they removed the multiple paths/solutions element from Dishonored.
The above can be interpreted one of two ways. Either:
- id Tech 5 does support more than one MegaTexture (up to 128k by 128k in size) for geometry per map. but covering a sprawling open world with detailed MegaTextures would blow out the file size of such a game to an infeasible level, or
- id Tech 5 does not support more than one texture for geometry per map and 128k by 128k simply isn't large enough to cover a sprawling open world without sacrificing finer detail
Either scenario could also apply to singular larger levels if they were labyrinthine enough, however I have my doubts that Dishonored 2 will feature levels much larger than those seen in the original.