Good stuff, actually, i was just about to start on this today. Having thought about it a bit more my approch will involve:

1. hook_form_alter(uc-object-options-form) to add a file upload for each option (although this seems a bit messy... any Interface suggestions? Maybe a new LOCAL_TASK altogether?). GUess this would make an entry in the {files} table for the image and a table (something like {uc_product_option_images}) would associate it with the {uc_product_options} table.

2. Some jquery work would be needed to change the large image when someone changes the attribute value with the attached image

3. Some how hook into the displaying of the product in the cart so that it used the thumbnail corresponding to the attribute selected (is there a hook for this?).

have to think about CSV importing when I get there, but I imagine there would be some hook to allow the this module to affect the imported CSV data.