I know XML and XSLT gets a lot of hate. To some extent, the hate for XSLT is warranted. But I have to work with XML files for my job, and it was pretty refreshing to not have to install any libraries to work with them in a web app. We use XML as the serialization format for a spaceflight mission planning app, so there's a lot of complex data that would be trickier to represent with JSON. At the end of the day, HTML is spicy XML, so you can use all the native web APIs to read/write/query/manipulate XML files and even apply XSLT transformations.

I suspect some of the hate towards XML from the web dev community boils down to it being "old". I'll admit that used to have the same opinion until I actually started working with it. It's a little bit more of a PITA than working with JSON, but I think I'm getting a much more expressive and powerful serialization format for the cost of the added complexity.