One of the major hurdles with using node editors is speed of development. To work well the editor must be fast and provide ample shortcuts and other speed up tools.

UE4 blueprint / material editor are nice examples of how you can make trivial tasks like branching or variable creation much nicer.

Allowing user to hold some button alongside pressing the mouse to create a particular node like a branch or a block.

UE4 Material editor (or Unity's Amplify) also allow to create a variable in place by holding a numeric key. I think it would be pretty useful if we could do something like:

1 + left click: create bool in place

2 + left click: create float in place

3 + left click: create Vector3 in place

0 + left click: create int in place

and so on. Adding a vairable and dragging it over takes some time, so that would definitely allow for faster iteration cycle.

As a sidenote in the creation - it would be nice to be able to convert a constant into a variable with some button / right click menu. Here's a canny for that

UE4 shortcut lists: