You make a great point about notations becoming more abstract for more advanced use cases, indeed this may be a "natural" process. However I'd like to add nuance with the observation that Bret may not be suggesting that we reverse the trend from abstract notation back to concrete visualizations. Actually I think he is calling for a rich variety of visual/concrete notations and symbolic/abstract notations that work in concert together to express our dynamic concepts, and extending those with the use of the dynamism of the computing medium to add interactive aspects to the notations (ala "Magic Ink").

His talk "Media for thinking the unthinkable" goes into detail on this, especially from minute 10 to minute 17: https://youtu.be/oUaOucZRlmE?t=600

The essay Magic Ink: INFORMATION SOFTWARE AND THE GRAPHICAL INTERFACE also goes into detail about this topic http://worrydream.com/MagicInk/