All great suggestions.
* Undo : Nice feature but not trivial. I will try.
* Pause the game with a button : Yes.
* Music continues to play if the phone goes idle : I will look at this.
* See where the new node will connect : that is problematic, the "clic+hold+move" is already used for removing nodes.
To let you know, my update (2 more levels+fast deletion) has been rejected by Apple because an information of price was in the app description. But it should be approved soon now.
Next version will implement your suggestions + a few more features I would like to add :
* Online editor + level download to test on your iPhone.
* Worlds : Different worlds to group the levels by their difficulty or theme. A different background for each worlds (the tuto levels in one world, hard levels, bubble levels etc...)
* Maybe new kind of items/moons but I have no precise idea right now.
Not sure when I can do all this, but when it's done, then I'll release a free version I think.