I agree this is going to be big. I threw a prototype of a domain-specific agent into the proverbial hornets' nest recently and it has altered the narrative about what might be possible.
The part that makes this powerful is that the LLM is the ultimate UI/UX. You don't need to spend much time developing user interfaces and testing them against customers. Everyone understands the affordances around something that looks like iMessage or WhatsApp. UI/UX development is often the most expensive part of software engineering. Figuring out how to intercept, normalize and expose the domain data is where all of the magic happens. This part is usually trivial by comparison. If most of the business lives in SQL databases, your job is basically done for you. A tool to list the databases and another tool to execute queries against them. That's basically it.
I think there is an emerging B2B/SaaS market here. There are businesses that want bespoke AI tools and don't have the discipline to deploy them in-house. I don't know if it is ever possible for OAI & friends to develop a "hyper" agent that can produce good outcomes here automatically. There are often people problems that make connecting the data sources tricky. Having a human consultant come in and make a case for why they need access to everything is probably more persuasive and likely to succeed.