We're working on a custom ecommerce project for a client whose requirements keep expanding every month. It started as a fairly standard online store, but now they want region-specific pricing, multiple inventory locations, custom checkout rules, integrations with several external systems, and eventually a mobile app using the same commerce backend. Building everything from scratch feels like a huge maintenance burden, but traditional ecommerce platforms seem too restrictive once you start moving beyond standard workflows. What are developers using these days when they need a commerce stack that's flexible enough for heavy customization without spending months rebuilding core ecommerce functionality?

The scope creep you're describing is pretty much the default with clients who don't fully know what they want until they see what's possible. The real problem with most platforms is that they're designed around a fixed idea of what ecommerce looks like, and the moment your client's requirements drift outside that box you're either hacking around limitations or maintaining a pile of workarounds that break every time the platform updates. The teams that handle this kind of thing well tend to go API-first from the start, keeping the commerce logic completely separate from whatever frontend or app layer sits on top of it.

Clients like this one have a way of turning a six-month project into a two-year one, and the stack you pick at the beginning either makes that manageable or turns it into a disaster. The composable commerce approach is what a lot of dev teams have been moving toward for exactly this reason. You can look at this tool https://medusajs.com/ . It gives you all the core commerce functionality out of the box while staying completely open to customization, so you're not fighting the framework every time a new requirement lands. Works cleanly across web and mobile from the same backend, which covers that app requirement down the line too.