Hmm... my company builds Shopify apps for large companies. We have had several in the app store that we maintain, that we're either moving to end-of-life or planning to.

Personally I believe the days of a solo engineer being able to build a viable Shopify app business are nearly over.

Shopify has instituted new process for assessment and approval of new apps in the app store, similar to Apple. We are finding the approvals can take weeks and sometimes require big rewrites to meet as-yet-undocumented business requirements.

Also Shopify stores can explode in bursts of traffic at a moments notice. And these apps sometimes are mission critical to the merchant's business. It is very challenging and expensive to scale an app rapidly when the folks who have installed it get large bursts of success without any forewarning. If a DTC brand launches their store with some cheap / free apps and their product goes viral, that means the indie solo app developer has to scale to meet the demand. These new DTC merchants often don't understand very much of the business of maintaining SaaS and aren't very forgiving when an app fails to keep up with the demand put on it.

The challenge is if an inexperienced developer offers the app for free or a nominal fee like $50/mo that means they have to scale up infrastructure and support and often re-write the app for a small number of merchants who are still only paying $50/mo. This happens to more Shopify app developers than I want to admit, and many many bootstrapped folks are operating at a substantial loss, looking for a way out without irking customers who depend on their app.

With that in mind, be very careful if you enter any type of SaaS marketplace. It seems tempting and low barrier to entry but you may be biting off much more than you can chew.