The Moto X Android is a superior phone but Apple has a following of loyal users who show no signs of switching. They like the user friendliness of the iPhone and for some people switching to a Droid is too much of a hassle. The Moto X will get some people to switch over that are looking for something new and looking for the features that Moto X provides but the iPhone 6 will not be killed over the release of this new phone.
Nothing can kill the iPhone 6 as it will still be strong and popular. Motorola has slid in the marketplace recently, and the Moto X will hopefully help bring them back into good standing with buying public. There just isn't enough momentum for the Moto X to "kill" the iPhone 6, or any other iPhone for that matter.
The new Moto X Android Smartphone has already been released to the market last year in a previous model and this is just a tweaked version with slight updates. In the cell phone market, Apple pretty much has dominated it because of their popularity. While Android is also really big name, it still boils down to brand loyalty. It took me the longest time to switch over to iPhone. Once I switched over, I went back briefly to an Android when I didn't have my iPhone and I had it for a month before I bought another iPhone. The make up of the brand product as well as the vast applications that Apple has available blew the Android away in comparison. The Android didn't have as many applications on the market as Apple, and while it is neat that you can customize the Android more to your personal taste, it wasn't enough for me to keep me in Team Android.
There are millions of loyal iPhone fans around the world. I don't believe that, no matter how amazing the alternative, the iPhone will sell poorly due to competition. I believe that if the sale of iPhones ever starts to truly lag, it will be due to a series of events, not just one, that brings the product to that place.