Shopify already!
This was brought up before, but I think needs revisiting since the last post was marked complete "questionable).
Integrate Shopify. Shopify is too big to continue to ignore. Sure Woo still dominates but Shopify is now running close second after passing Magento in 2018. (source: https://www.cloudways.com/blog/top-ecommerce-platforms)
Many RS subscribers need two-way sync with RS inventory, POS and eCommerce. Both APIs from RS and Shopify are out there ready for action. RS is a great product and we love it's diversity, but it really falls short ion this area. Zapier is limited for RS as well.
It's time!