After spending a bit of time with Dialogue Designer, I have to say that I'm very happy with the program. Matt, I'm not sure how active you are in updating Dialogue Designer, but I thought I'd provide some feedback:
Being able to easily duplicate nodes would be a huge quality of life improvement. My suggestion would be ctrl+left click and drag to duplicate a node.
Choices: It would be really useful to be able to change the order of choices by dragging them. As most engines will use the order to loop and display to screen in order, being able to easily change the order would be a big help, as right now it requires deleting choices and rewriting, and relinking. It's a major pain when you realise you need a new choice at the top of the list.
Renaming characters. Currently, any change to a character name requires a new entry, which means that every node they speak on must be manually changed. Ideally, this could be changed at the character panel with changes reflected automatically across nodes. Renaming variables would be a similar improvement, but only if it auto-updated any node references to the changed variable.
Ability to add additional values to nodes would be useful. I'm currently using slide_camera as a boolean checker for animation control, but it would be nice to be able to rename it or add multiple checks.
Start node is not always index 0 which is annoying as you need to loop through the json to find the start block
When removing languages from a project, they are not removed from choice branches.
Overall, I'm really happy with DD. I'm hoping it continues to get the support it deserves.