Great news!! For now I saw the you can let the user create a node "Tee shirt" for exemple and then it is possible for him to upload his design.
It would be usefull to let the admin of the site custumize the checkout section with others fields.
Also is there a way to autofill the check out section (like the address and the name)? I think it's possible with webform ....
These are just a few ideas (nothing new really) but the ubercart module is great anyway