When the Kinect device first launched on the 360, it was a tool that was designed to work with a handful of games. That list of games didn't grow dramatically over the rest of the 360's lifespan, and with the exception of hidden gems such as The Wavy Tube Man Chronicles, there weren't very many must-play titles that required Kinect. Fast-forward to earlier this year, and in the middle of Microsoft's PR nightmare that was the Xbox One reveal, it was announced that not only was the new model of Kinect required for the system to function at all, but the device would always be on. Several Internet protests, public mishaps, and backpedals later, Microsoft announced that while the Kinect would still be packed with the Xbox One, it would no longer be required for the system to function.
As a result, you can still see the remnants of Kinect-required commands in most of the launch titles: microphone icons next to menu options in Dead Rising 3, the ability to speak "I promise" as a menu joke in LocoCycle, and so on. All of these titles have now made these commands optional, since they can't depend on each and every user actually having the Kinect plugged in and running. It's this lack of necessity that's ultimately going to make the Kinect a relic within the next five to ten years.
If the lack of Kinect functionality in these launch titles is any indication, the future is going to be more of the same. Sure, there will be titles specifically designed to work with Kinect, but those are going to be few and far between, especially in the first two years of the system's lifespan. The drive during these years is going to be selling the system itself, not the Kinect. That means Microsoft and third-party developers are going to have to place an emphasis on software, not hardware. Games are what's going to sell the system, and that means the Kinect is going to take even more of a backseat than it already has.
With the exception of games aimed at children and younger players, and party games such as the Dance Central series, the Kinect is going to find itself marginalized. As we get further away from motion controls as a fad, Kinect is going to look antiquated--something that appeals only to your friends and family who don't really pay much attention to games. This is unfortunate, given that the new model of Kinect seems substantially more powerful than its predecessor. There's a lot of potential in that device, but I can't help but think it's going to end up as nothing more than a powerful webcam (if Twitch really catches on with XB1 users).
When Kinect was a mandatory part of the Xbox One experience, Microsoft and other developers were free to incorporate it as much or as little as they wanted into the design of their games. Now that it's nothing more than an option, it's going to become less and less of a priority. Not to mention the fact that a serious dud of a title could bury the device completely. With this new Kinect model, Microsoft literally can't risk having another Steel Battalion on its hands.