The way we work with text makes it easier to construct and layer abstractions. Having twenty thousand different boxes in a graphical language is not something we're used to in a way we can have twenty thousand different words in code (or in a sentence) - and if you start treating boxes as letters and grouping them, you're essentially inventing a textual language right there.
I'm not saying visual programming is a dead end - but I feel we need a much different style than just boxes with arrows. For one, text seems to exploit human ability to pattern-match much better than box diagrams; that's why we feel text is denser in information. Making diagrams more information-dense is not an area I recall to have seen explored in visual programming, but maybe we need to go there.
Anyway, best luck with the work on FMJ!