Maybe because I am out of loop with web development, but this sounds like a huge change to me. So instead of HTML elements, there will be just one big element, and everything will be rendered there? How will text selection work for example? Will Google Docs basically implement a GUI library like GTK, which renders everything itself, but for the web?
As if fate tries to prove a point, I recently struggled with a random ass google docs document and just wanted to download and import to use in my own spreadsheet software. There probably would have been a Google Approved way of doing it but if there was, they intentionally made it hard. I ended up copying the HTML somehow. I guess that will no longer be possible in the near future.