I was excited to hear this was coming to 4.7, but have to admit, couldn't immediately think of any suitable use cases.
Perhaps "art directed articles" would be a worthy use case. There could even be different premade templates for different styles of art directed article. I'm not sure how trendy they are anymore. They seem to have peaked a few years ago, but I still see them sometimes today.
For a "portfolio" post type, I could see different templates being used for different types of portfolio items. For example, a "photography" portfolio item might include a photo gallery, but a "writing" portfolio item might include stylized chunks of text. Or maybe just different layouts of photo galleries.
That's all I got for now. Might think of some more later.
With all that said, I honestly don't think I've ever even used page templates in a publicly released theme before, so I don't really see myself using templates for different post types either. It's nice to know the possibility is there though.