In my mind there is no contradiction to release XIV this friday, and to show XVI next week.
Why would there be a contradiction? You get attention on yourself by promoting something people can't have right away, and if you have a product that is readily available, it encourages sales. You think Apple holds back it's iPad when they reveal a new MacBook? Square Enix may stagger releases, but from a marketing perspective they have no fear of overshaowing.
By getting everyone excited about Final Fantasy without being able to actually have the new Final Fantasy (for 6-7 months at least) you open up the door for people to join or re-activate their XIV accounts, while also getting many pre-orders.