I think abstraction is already well represented in photography (e.g., Man Ray, Minor White, Moholy-Nagy, the later Walker Evans, etc.) , without the need for digital, though it may offer new possibilities for arranging color, light, and dark. Ever since the invention of photography, there has always been much exchange between the language of painting, photography, illustration, advertising, and later cinema.
Even the tools of photography and painting have not been mutually exclusive, as painters have long used optical devices for rendering the three-dimensional world in two dimensions, and photographers have idealized subjects with pencil and brush.
What is specific to photography?
Some (usually citing Walter Benjamin) point to reproducibility, but I'm not convinced of that. Sculpture had reproducibility thousands of years ago, and there was engraving of various forms well before photography, and many 19th-century photographic processes did not in fact involve reproduction of a positive from a negative.
Unlike painting, however, photography does require the presence of an object that is photographed. Even a photogram must have something that casts a shadow. Even an image that completely abstracts, distorts, and defamiliarizes the object on the other side of the lens requires the presence of that object.