Not sure I understand your request correctly but why not just add a folder or something with a custom icon (maybe an empty icon) and as display name something like "==============" or so? Creating a dedicated object type for something like this feels like "overkill" ;)
I would like to suggest a new divider "element" that we could add into navigation pane to divide other elements. Like a divider line or a rectangle block (maybe even with a possibility to change the colour or it). Don't know how to explain this idea in a more simple way but just like a <HR> tag in HTML language or like a simple line element. Don't know how handy this element would be to the other users but I would sure like to have it. I imagine it can't be that hard to implement it..