"How should the customer get going if they accepted an order to develop an IntelliSense feature?"
Okay, wait, let me see if I understand this.
Your customer signed a contract promising to deliver an IntelliSense feature, but they don't have any idea where to start, and they're asking Microsoft to help them either by providing an API, or helping them find somebody who has a ready-made solution.
Apparently, this is what happens when people who grew up with StackOverflow get a job.
The customer needs to grab a blank piece of paper and start designing some software.
This kinds of sounds like my previous workplace in my home country.