So the solution is that both Shopify and Wix should let the user edit those files. That's it.

Agreed. In a perfect world, they would. But I cannot merge PRs into Shopify's core. Waiting for trillion-dollar corporations to change their security models is a death sentence for a new protocol. We build for the infrastructure that exists today, not the one we wish for. When they open the gates, we will move. Until then, we live in the root.