GPT-3 can do a good job of this all today, without any additional training.
An expert could help out by providing a few example prompts, but the result would be a lot more powerful and require a lot less development work to put together than trying to build some kind of placeholder wizard from scratch.
And the madlibs is free to use, for everyone.
All things considered, GPT-3 is a more of a shibboleth of AI revolution than an actual one. Much better to give models like GPT-NeoX to talented development teams who can really optimize and fine tune it, attach great sampling strategies to it, and create great products from there. The API is just too limited for me to want to build a company atop it.
If no-one has built the madlib template for "a letter to the council asking about my disability benefits" then madlibs being more predictable isn't going to help you.
Here's one that I find personally really interesting:
Imagine you have a disability, and the government agencies responsible for helping you have denied your claim. You need to write them a letter. You don't have much (if any) experience writing letters to government agencies, so you're finding that task challenging.
GPT-3 can write that letter for you, and it will de a really good job of it.
Of course, you need access to GPT-3 and you need to learn how to drive it with prompts, so this isn't necessarily an easy thing. But I think it helps lean in the direction of the kind of benefits people can get from this class of technology outside of just playing with the AI.