The reason for writing a new editor is to extend the things that can be build with the Scratch/Blockly one, like frontend interfaces or, in the future, streaming flows. There were also some recurring problems people found when building with Scratch that we can solve by having total control over the editor, like reacting to type mismatches. (Note, though, that Scratch also supports type checking)

I'm really interested on other viewpoints on visual programming, so for sure I'll send that email.