I think one thing to think about is really anything around language. Law, content, customer interaction (email, marketing, etc.). What I really see as the big opportunity here is using it as "glue" to integrate separate APIs and then add UI polish. Doing the thought work of "Oh, if I combine this API with this prompt and then send the result to this other API and use OpenAI to reframe that result and then put a UI on it..." is what is going to make your solution stand out from every other "AI Blog Writer" or "AI Email Spammer" or whatever else.