I definitely agree with the ‘if it hasn’t been released, don’t show it’ view. Even if it’s not in the same sector of design, it’s a small world, and a small world of designers who talk to each other! I once interviewed a candidate who stated talking about unreleased product, they even started the line with “I probably shouldn’t talk about this, but…”, it made it worse that they knew they shouldn’t be talking about it, it didn’t give me much confidence that they wouldn’t do the same with any of our work!! An NDA is the same flag for me.
I think most employers will understand that you’ve worked on products that have been dropped or shelved, it’s all part of the design process. I’d agree with Yo, beef up your portfolio with alternative examples of work, or even demonstrate how you work as well as what you’ve worked on. I spent about 6 months concepting around 360 ideas recently… and not one concept made it to development, but they’ve all been archived for the future, so I’ve tried to show how I concept and how I typically work, and hope that that can somehow show as much as a concept!