Apple has released a statement saying certification for HomeKit compatible hardware has been ongoing for the past few months, and the first wave will begin hitting the market as early as next month. From The Wall Street Journal:

"HomeKit [hardware certification] has been available for just a few months and we already have dozens of partners who have committed to bringing HomeKit accessories to market and we're looking forward to the first ones coming next month," said Apple spokeswoman Trudy Muller.

HomeKit was first unveiled during Apple's World Wide Developers Conference (WWDC) in 2014, and gives iPhones and iPads a standardized method of configuration, communication, and control of "Internet of Things" devices like smart lightbulbs, appliances, and more. Users can, for instance, control their home using Siri, and group different rooms in their homes into "scenes".

A number of hardware companies have already announced HomeKit devices, including iDevices, Elgato, and GE.

We saw many of them at CES 2015 back in January, a show that often serves to preview hardware retailers will have on the shelves in time for the holiday shopping season. June, which conveniently enough has a WWDC 2015 keynote already scheduled for the second week, would be more than early enough to meet those needs. It would also be a tremendous stage from which to show off even more Apple Watch home automation control.