Decoupling content management is a trend that has been a megatrend for quite a few years. While most web sites are still built using the CMS itself, the rich content feeds allow the content to seep through to web and mobile applications.
For eCommerce a similar trend is not as prominent, rather people still observe eCommerce systems as monoliths. But nowadays it's more evident than ever that microservice architectures offer some advantages over such approaches. Instead of honing a content management system to include a half-baked eCommerce module, developers should be looking at the best-of-breed eCommerce system to integrate to their CMS.
Already today there are many credible options for Decoupled eCommerce projects. From open source efforts to SaaS operators, you can already break free of a CMS driven eCommerce experience with eCommerce APIs. In cases where you have a content driven website that has product integrations this is an ideal approach as you don't get any compromises.
Some options for creating decoupled eCommerce backends using contemporary PHP are Sylius, Magento 2 and Prestashop: