XML language is so year 2000.
We don’t use it anymore in the professional world. Slow, inefficient, and difficult to read.
Want to save CPU time? Get rid of it!
We in professional work ?
Strange, I use it all the time. With Notepad++ not difficult to read at all.
Hmm I must be doing something wrong
I suggest you just stop using it. Let us slow non-pros use it
And English too. It’s so year 1500.
Editing the Expression maps is a royal pain.
If you are a Professional Software developer and you’re okay with XML 
But if you say so…
So this is your true beef with XML which you did not mention at the outset.
What are your option besides XML then?
In my own view, if it’s editing the the bare file that’s the subject, e.g., SomeMap.expressionmap or Key Commands.xml, once I learned the format I could edit things fairly comfortably. My experience with json comes via Keith Macmillen devices, which store settings and presets in that format. That’s also doable.
xml has more words, but if I use an editor that highlights the code like PSPad, it’s sometimes even a little easier to focus in or dart to the next parameter of a given type (say if you’re wanting to change a value in all of a certain CC or such)
I read the page linked by the OP too, and even there it seems like a draw, each is a tool with its purpose.
XML and JSON are both widely used in the “professional” 
world. They have advantages and disadvantages. JSON is popular for message transmission, but XML is popular for document representation, which is how it is generally used in Cubase. In any case, it is unlikely to be a significant factor for performance.