Theory 1
Each film has the same amount of words in the title in relation to their part in the trilogy. For example Episode I and Episode IV, both the first respective films of their relative trilogies, have three words in the title. The Phantom Menace and A New Hope. Both Episode II and Episode V have four as do Episodes III and VI. So we can conclude from this that Episode VII, the first film in the new trilogy, will have three words in it. And that the second and third instalments will both go on to have four word titles.