This doesn't make sense. JSON is used because it's a handy data interchange format, but it doesn't mean it's the best tool for every job. XML is a document markup language that is much, much better than JSON for describing interfaces and alike. And even then it's not really ideal for describing control flow and computations that are needed for any meaningful app that is not a static page (see XAML, AngularJS, FXML, - they do have some power but they're still tied to real programming languages: C#, Javascript, and Java, respectively.)

And all computers and devices made in the last century have no problem dealing with XML, HTML, JS over the wire - in fact this is exactly what web browsers have been doing. So even though you're dealing with native iOS apps and not webpages, that doesn't mean you can't use a similar XML format(or any other document markup language) along with a proper scripting language. And if you insist on staying close to JSON, you could go an all JS approach and use JS(instead of JSON) to describe your views, and also be able to embed JS computations - this is exactly what React does, and does very well.

And again, JSON is not a document markup language, so optimizing it for displaying documents/interfaces seems futile when you can just use XML and save yourself and the interpreter some pain.