I'll take your YAML or XML or whatever and raise you ASN.1. Heck, you could mount sysmibfs and make it legible - hilarious!
The latest modish markup thingie isn't going to solve the design goals of sysfs, let alone anything else.
I personally like the simple text file with a value in it approach - I don't have to learn Yet Another Markup Language (and I don't just mean YAML 8)
Re evaluating the goals and perhaps filling in the missing ones and then someone enforcing the end design decisions will give a chance for the grandkids to see this thing.