Krita has fit to width, fit page but doesn't have fit page to height. This would be useful if the with of the image is much larger than the height like in a 2D side scroller game.

I could do this myself if I can get to compile Krita myself some day. This feature should be fairly easy to do I guess.

It wouldn't be that hard to do, though the code is spread around a bit because of Krita's history as a KOffice/Calligra application. Building Krita is easiest on Linux.