The Wing Box set is now in production and being shipped. It is available in the e-shop both on its own and in a discounted promotion combo with the Spine set (go to Now Shipping to chose which), the Combo item is KAZ007HAS). All items are currently in stock, and the web article on its assembly will be up shortly.
The Wing Box set includes both complete boxes, left and right with more than what is shown here. The instructions can be viewed from the product page in the e-shop and downloaded as a pdf.