I fully agree with shift studio. As 1 unit is thought of being 1 m in Cheetah (at least as long as you stay out of space and the microcosm), 1 pixel = 1 unit would be insane for most people. So something more convenient for the majority would be more reasonable. After such an import you still could change the size, so no problem even if you need this pixel=unit-ratio.
Again like shift, I fail to grasp 'pixel-perfect-ratio'. For a background-image? For a blueprint? I don't mean any disrespect, but I'm used to speak as I think, and for me it doesn't make any sense. In the first case it's dependent only from the render size, in the second case it makes even less sense.
Pixels are only important for the render and for textures in 3d. The pixel-size of a blueprint is not important inside Cheetah (of course it should be big enough for you to model after, i. e. it should show the necessary details) as we try to simulate things that do exist in a real or fantasy world. If I would model myself for example, I would use my size in units, as the resolution of a picture of me doesn't have any relation to me. Say, my photographed self is half as wide as the full 4k-picture, a 'pixel-perfect' model of my person would be 2 km wide... See, what I mean? And even if I would use a small picture, model after that, I'd scale the picture or, later on, the model. If the pic is too small in Cheetah's window, I just zoom in. Problem solved.
And just for the fun of it. Think about a small picture, say 200 px wide, of the Eiffel tower, I'd want to use for my self-portrait as background. I'd be 10 times as wide as that thing (which isn't 200 m by the way). If you do use pixels in 3d instead of real world units like cm, m etc. you get all kind of weird problems and nothing will fit together.
So, I really would like to know any scenario where this concept is useful.