I think you missed the point here -- the great thing about author's "oj" here is that it takes existing document, with any format, and makes it look nice, in a fully automated way and without changing semantics.

(I am talking about "Human Style with Colors" here -- this is the cool part, and I don't really expect SEN to take off except to display things on the terminal)

That tabular-like alignment was generated automatically -- I can take any existing JSON data source and the program will automatically make it look nice while not requiring any changes in the consumers or producers of the data.

Compare to Tree Notation, for example this code: https://jtree.treenotation.org/designer/#standard%20iris has this block with has a clear structure:

    sepalLengthCell
     extends floatCell
    sepalWidthCell
     extends floatCell
    petalLengthCell
     extends floatCell
    petalWidthCell
     extends floatCell
    speciesCell
     enum virginica versicolor setosa
     highlightScope constant.language

This looks pretty ugly to me. There is clearly the table-like structure, but it is hard to see, because each line is split in 2. If this were JSON/SEN, I could make it look nicer:

    sepalLengthCell: { extends: floatCell }
    sepalWidthCell: { extends: floatCell }
    petalLengthCell: { extends: floatCell }
    petalWidthCell: { extends: floatCell }
    speciesCell: { 
        enum: [virginica, versicolor, setosa]
        highlightScope: constant.language
    }

See how it's all aligned now and how structure comes out? And all at zero effort from my part, it was all computer generated? But with Tree Notation, the above is invalid -- it has different meaning, so the compiler won't accept it. You have to use much uglier vertical method, with all the newlines.

And Pretty JSON can also adapt to display width. Someone with large fonts or small display can request 80 characters wide output, and "speciesCell" will be wrapped. Someone with huge display can request output 250 characters wide, and "speciesCell" will be column-aligned with others. Another thing which is pretty impossible in Table Notation without a lot of work.