I'd like to see how that worked. In my mind I'd guess such a feature could have been great for one column layouts, like in this website, but I can't imagine how it would be for the then-traditional layouts of a left sidebar navigation column and a right area for content.
Page starts zoomed out. Each element is limited in width. Double tapping on an element (e.g. a paragraph) zooms in on said element, making it full width. Further zooming in causes the text to reflow to the viewport width. It's difficult to describe, but it used to work fine.
