My thesis is that Shopify (SHOP) is under-monetized with a flywheel in full gear such that future economics will be extremely different from what we see today.
Looking at the competitive landscape, BigCommerce isn't yet public. WooCommerce is a WordPress plugin and it requires some do-it-yourself work on the front end along with integrations on the back end. Demandware was acquired by Salesforce (CRM) in 2016. Magento was acquired by Adobe (ADBE) in 2018 and CEO Tobi Lütke answered a question about them in the 2Q18 earnings call