Since JSON shows a lot of benefits over HTML, why don't just abandon HTML? Qt frameworks with QML shows it is perfectly possible to use JSON to design rich content
EDIT:
Many of you think about this question in terms of performance vs html but i'm not about that.
HTML is just less readable and it's not enough per-se to describe UI behavior, look and feel. Maybe a technology shift is needed. I think from the developer point of view.
What about a browser capable of rendering a QML like web-page for example? QT with QML uses google V8 engine to do its work.
If you can write a web page in a technology that is not HTML, people will start using it. Browser could support HTML for a long time and allow developers to code with less stress