There is a limit to how thin they can make the cogs and chain links before they become completely unreliable. The next move would be to move road bikes to the same 135 OLD as mountain bikes, so that they can keep the same spacing as 10 speed, but add another gear. Obviously, short chainstay designs would make the chainline a little more wonky than it is now, but I wouldn't be surprised if they are at least looking at it.