As big an issue as the resolution cap may seem, one modder—NeoGAF user Durante—has already fixed it. In fact, he fixed it before the game had even come out, by looking at other games that use DirectX 9 the way the Dark Souls port does.

It's simple: just download the files and drop them into the folder where Dark Souls is located, and suddenly Prepare to Die Edition becomes the visually stunning, 1080 HD version it should have been to begin with. Problem solved!