It's interesting to see how many focus on the nested, recursive representations of expression and statement syntax.
It's understandable for teaching the concepts of syntax to people learning programming for the first time, but I don't think it tackles any of the essential complexity, or what makes programming hard.
It keeps getting reinvented in different guises, often with an air of democratizing coding, taking it out of the hands of the high priests (IT) and into the hands of the people. But what's hard about programming isn't if-statements, loops and assignments. It's incorrect assumptions and broken invariants, usually in runtime data, generated by code which is often distant.
Relatively few interfaces seem to deal with manipulating data rather than code. I think working with data is more likely to be useful and successful. Look at things like Visual Basic - a form designer is effectively manipulating a stored data structure which defines how a runtime data structure is going to get constructed.
I wanted the basic elements of the interface to be at a higher level than individual characters. The nested squares style rendering is highlighting grammatical structures in the language—not to teach syntax, but just to indicate where an interactable UI element is, the same way you have rectangular bounds around a button etc.
My motivation for this was to make it easier to manipulate code with lower-precision input devices (e.g. the microsoft kinect / leap motion), but I think there is general interest because a lot of the people writing these editors start from the premise that interacting with the AST directly (as opposed to character sequence) opens up doors, and nested squares is just kinda the most natural/obvious way of rendering an AST. It's also a more natural pairing with the input style of many of these interfaces (e.g. Lamdu[2] or Fructure[3]) which also operate at a higher level than character sequences.
The alternate rendering in itself isn't world-changing, it's the underlying change to directly manipulating a model that then gets rendered (as opposed to parsing the interface—i.e. character sequences—in order to arrive at the model) that's important.
(And even it probably isn't the most important revision to programming tools in general—but that doesn't make it not worth working on if someone's interest is in that direction.)