A lot of support for it is there and more has been added over time. There are still a couple significant places where support for oriented images is missing. I believe ImageReslice (a replacement as backwards compatibility turns out to be tricky) is one of the big ones and is on my todo list. I’ve been sort of avoiding it as in the back of my head I want to create a new image data class that defaults to cell data (or add a flag to the current class).
People think of pixels as cells and our current notion of pixels as being point samples creates confusion. People tend to expect 100 pixels at 1mm per pixel to create an image of 100mm, but in VTK 100 point samples on an axis equals 99 cells on an axis. And when you draw those cells they look like 99 pixels when people expect 100. I think moving to cell data for pixels would get us to a more common representation. The image would have 100 pixels of cell data, 100 cells, and 101 points defining the boundary of those cells (on an axis).