I’m a big fan of JTBD and I can understand the challenge of trying to get the right information out in an interview. What I’ve found works really well is getting people to talk about what they do today in terms of a business process.
I’d agree that it’s best to focus on new customers… or even those that haven’t yet started using your solution.
I get them to talk about what they do today and why and map this out in a process. People always find it easier to talk about what they’re already doing and without realising it they’ll be telling you all about the challenges they face and the things they think will make their lives easier. This is the stuff that will help you make your product stand out.
I don’t just do one-to-one interviews, I’ll get a group of people in a customer together and map the process in a collaborative workshop so you can see how they challenge each other and how they view the same challenges in different ways.
We’re actually a business change and transformation practice but my background is in product so I still regularly consult for product companies helping them review their product. I’ve found the tools we’ve developed for business change management also work well here for analysing and understanding what drives users to use your products.