The ability to preview clothing items on your character is a great asset when deciding whether to purchase that pair of pants or shirt - seeing how it goes with your other clothing items can definitely influence the decision.
With that in mind, I think it would be a good idea to allow non-subscribers to preview the subscriber-only gear in the shop. Instead of only showing the cost, it could also show "Subscription," and clicking on the purchase button would take you to the subscription page, and then return you to your cart after you purchase a subscription.