The problems that XML and XSLT address have not gone away. It saddens me when the XML-hating JSON community starts reinventing solutions that have all the same issues of bloat and complexity (see JSON schema, Collection+JSON, Siren, etc). I would not be surprised if someone soon announces a "JSON Transformation" tool that can convert one JSON schema to another. Followed shortly by a standard for JSON namespaces so yo…
So does mustache, with a bit less resistance/overhead.
So does Polymer if you make your xml tags into web components and apply them. It also has all of the benefits of Polymer's isolation.
I think xsl was and is a good idea. I just think that other things have come along that are easier to get into.