Something to crush Doordash, Instacart, Uber Eats, and all other delivery apps. Made in a flexible way rather than overconstraining by specifying food items within app. I have made a number of notes on this and shared ideas for how to mitigate counterparty risk via relational contract theory, as well as why I see this as an ideal application for Nostr. Happy to discuss further or find the notes I have made if you're interested.
Selling the sort of content you are thinking about doesn't seem all that useful. If you want it design focused, something to compete with Fiverr and UpWork, which can include graphic design is likely a better option.
All these things have tricky reputation problems to solve. The goal is to get real economic markets that actually matter on Nostr, and high res AI images that are not made to order not all that relevant.