As a one-time Shopify user, I'd think so. The default model is recurring billing and Shopify's features are super bare bones with the "there's an app for that" fallback that keeps the platform viable. The apps on offer are very hit or miss and many are simply poorly designed or thought out, and there seems to be room (in conjunction with some marketing) to carve out a good space there for quality interoperable apps.

I had built a couple of Shopify apps early on that ended up generating about ~4k/month, and I ended up selling them for seed money for my next adventure.

It's a nice way to make passive income, but I wouldn't try to make a business out of it. Remember you are still on somebody else's platform, playing by their rules. It's fairly easy to have the rug pulled out from under you, so don't put all your eggs in that basket.

I have a Shopify app that makes ~$400/month gross revenue. Do your research first to make sure that you're filling the right niche, and you can definitely do alright.