doubt I would use it elsewhere instead of JSON but if this is an indicator that .plist in xcode will go away then I'm all in - .plist is probably one of the worst formats human can work with.
NeXT used a text format for Plist[0] (which Amazon’s Brazil Config looked very similar to) but was deprecated relatively early in OS X’s lifetime. All of the plutils can still read it, but none of them will write it.
The biggest drawback was limited number of types, imho. It seems like encoding issues were another drawback which led Apple to use XML when OS X launched. JSON want a thing yet, so XML probably looked like a good option.
