If it was actually using XML as a markup language then that would be a reason to stick with it. But XML seems to be complicating things much more than it simplifies.

>> XML remains the best format for representing trees—deep hierarchies of nested data. JSON handles flatter structures well, but good messaging protocols are extensible: extensions can be embedded at different levels and composed together, like Lego bricks. That’s where XML shines.

Anything reasonable you'd be doing with messaging protocol is pretty flat.