How to seperate products images folders based on product display categories?
What you are proposing to do won't really work since you cannot embed tokens within tokens. You're going to need to split the images up based on something else. Here are some options:


Product type [commerce_product:type] (e.g. "shirt" - I haven't checked this one.)
Date [current-date:custom:Ym] (e.g. "201512")


Furthermore, unless you have hundreds of thousands of images, you're likely not going to see much of a performance degradation. If you do have that many images, perhaps you should consider using a CDN or some external system to offload image handling.