I just got pinged by this topic yesterday when I worked a bit on this integration.
I have something working atm, but I started refactor a bit and then customer wanted to prioritize something else and this got shelved, again.
Anyways. What I've figured, this is somewhat easy to implement. However, the level of customization (and the 'ease' of it) my customer requires made it a bit more difficult to implement all elements' parameters, positions etc.
So I created custom entity for elements and their properties. Out of these elements we build commerce_product which holds all image and text elements and their parameters. These products, when added to custom product display node are parsed in hook_preprocess_node + tpl file to html5 elements required in JQuery tool.
Then the JQuery tool loads created product back to backend via ajax, and another type of commerce_product which contains all the info + images from the designer and can then be purchased by customer. Those customer products can be listed in customer info page and be purchased over again.
What I need to do as well, is create method for my client to export created products to printable pdf files. And there I'm stuck now. But I don't know when I have time to work on this again..
Just thought to share some thoughts on the issue while I was at it.