It would be cool to have the design that the user made available for upsell so they can purchase the design on other printed products. I'm using this for t-shirts and I'd like to be able to automatically put that same image on a bag, hoodie, or pillow and ask the user to add them to their cart.

I Believe that you could do this 2 different ways but I could be wrong.

1. If is apparel have variations with different prices for Tshirt or Hoodie while keeping the size attribute which would be the same.
2. Creating a new product under the same category inside fancy and creating the woocommerce product as the art itself and adding the price difference to the fancy elements for the different objects like tshirts, hoodies, cellphone cases etc and selecting that category for that design to enable this. 

Again those are quick ideas that came to my head.

Yes! I would like to do exactly what you are asking for as well.

Hello, i like this idea . i think its even natural process with those type of trading, i saw this function in so many places.