I think it's difficult to say how many merchants went from hosting their own e-commerce site that engineers built for them from scratch, and transitioned to Etsy, Ebay, etc., laying off the developers they hired in the process. Without numbers to back myself up, I would say that there are certainly many more developers and engineers working on E-Commerce today than ten or twenty years ago. Services like Stripe certainly help businesses focus less on setting up common parts of a website or online business, but that just leaves people more time to focus on the "business logic" that is unique to them.

The "current stack" may certainly be ripe for disruption. But I'd predict that rather than put developers out of work, it will simply bring even more businesses into the fold who may not have had the resources for developing their own solutions beforehand. There will always be companies with the resources to demand custom solutions to fit their particular business needs.