The app is set to arrive with the launch of Apple's next version of iOS this fall. That's likely to be called iOS 10 and will almost certainly be seeded to developers at WWDC in June.
The information was found in an interesting Amazon review, posted by a person who claimed to work in marketing for Apple.
As I work in marketing for Apple, we test many Smart Home devices, especially for iOS HomeKit integration. [...]
Some advice, there are many third party applications, most free, that offer more control and customization(s) with many Smart Home devices. "Yonomi" is a free app that I often use, "Home" is another which cost $14.99. Both offer support for many devices with more added daily (including Amazon "Echo"). The next version of iOS due this fall will have a standalone "HomeKit" app as well.
MacRumors was able to confirm that the reviewer does indeed work at Apple. This is likely the closest to a confirmation of an app launch that we're going to get.
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