Some thought of unknown worth..
I note that eBay.AU developed a free addon for wordpress's Woocommerce.
My research indicated that the WP/Woocomme thing was very much not a great way to go.
So I'm thinking it may be better to get eBay dev itself to write an addon for CSC rather than CSC for eBay.
Perhaps eBay would then have the resources to keep the addon updated each time they change the API operation.