I don't believe there is a major leap to be made. Here's why.

There have always been visual editors for the web. As the author suggests, they have relied on abstractions of the underlying code. For example, the CSS box model (width/height, padding, border, margin) are often abstracted as draggable handles on bounding boxes. Yet these systems suffer from some fundamental limitations:

1. They obscure the underlying implementation, making it harder for designers to understand and fix problems when they inevitably occur. On a related note, the lack of visibility into the code inhibits learning.

2. They lack the power to express more advanced styling rules, such as the following:

  /* Paragraphs have 20px margin above unless they follow a heading */
  p {margin: 20px 0;}
  h1 + p {margin-top: 0;}
  
  /* Don't indent the top-level UL, but indent 20px for each level of nesting */
  ul {margin: 0;}
  ul ul {margin: 0 0 0 20px;}
  
  /* Divs that are immediate children of forms get 20px margins, but divs nested
  within those don't. */
  form > div {margin: 20px 0;}

Or, if they do have the power to express those rules, they're doing so in one of two ways: Letting you write CSS ad-hoc, or building a complex GUI that maps to those CSS rules. In the former case, you're back to hand-coding. In the latter case, you're using a clunkier proxy for hand-coding.

3. They lack the power to express idiosyncratic JavaScript interactions. They can provide some generic primitives like rollouts. But many, many real-world apps need fine-grained control over interaction. For example, today I built a system of nested lists with sorting, deletion, and insertion to arbitrary depth. It was so idiosyncratic that it couldn't have possibly been made into a generic component in a visual editor. Problems of that nature are fairly common in my work. And no, the idiosyncrasy is not a sign that something's wrong: Different problem domains often call for (slightly) different interfaces.

4. They don't play very well with dynamic websites. If you need forms or for HTML to be generated from a database--both of which are very common needs--you can't express that generically in a visual editor. Expressing that kind of logic is an act of programming. Historically, efforts to abstract programming into a visual process have been disappointing or outright failures. Source code is the only workable way to express a computer program.