One of the things when creating more complex boards is that certain structures appear in many locations. Right now the only option to work with that in RTB is to copy-paste the structure (most likely after grouping it) in the board. When you then need to update a detail on that repeating structure, you need to update everything- over and over again..
Allowing a 'source' (grouped) item to be cloned/repeated in such a way that editing the original is reflected all over the board in all clones would be hugely helpful.
Since it's so abstract, this feature would be extremely helpful in a wide range of problems.
I'm creating mockups of screen designs. I want to design a new button and the font, icons, colors are set. Now in the board I want to use that new button in many example screen states. If I change the 'source' button to have a better color, or change the icon, than this change would reflect all over the board.