This video helps to explain Shimano’s new D.R.D. optional standard. According to Shimano, this new standard helps provide crisper shifts, greater durability and easier wheel removal and installation.
One of the main points that Shimano wants to get across with the D.R.D., is that they are not forcing this standard on the industry, and will still be making standard-mount Shadow Plus rear derailleurs. Also, the bike manufacturers offering D.R.D.-compatible frames will, in most cases, just use a different-shaped (replaceable) dropout or derailleur hanger to accommodate the standard.