You speak of pixel ratios and prezooming in the same sentence, and I am confused. Those are two unrelated concepts. Are you asking for an option to set a starting zoom level (e.g 2x, 3x, etc instead of 1x) for your submissions, or for an option to change the pixel aspect ratio (e.g. upload a piece with square pixels but set for it to be shown with wide pixels)?

If you're asking for automatic zoom: That seems like a nice option, and it would save people from having to write "best viewed at Nx" in the description. I support it!
An issue I see is people would have no way to know whether a piece can be zoomed out or not, but I suppose if this feature becomes available, pre-zoomed images could simply be made against the rules instead of being merely discouraged, which means that any time a user sees a pre-zoomed image, they can expect to be able to zoom out.
Unfortunately, I have little faith that it would be implemented, since it requires modifying the backend (to save each submission's default zoom level), in addition to the front end.