I think Apple will unveil it at WWDC alongside advancements in Siri and new APIs, and say that it's launching in autumn. This will give developers time to add support for it ahead of launch. Apple will again show it at the autumn iPhone event, maybe show something "extra" about it, and announce the pricing/release date info.
I tend to think that Apple will price something like this in the $99-149 range, and will want you to buy several for your house. I think such a device will also act as a mesh WiFi network, enabling better coverage throughout the home. This device will also act as a HomeKit hub, and having them scattered around the home will also increase range for bluetooth smart devices. It will also act as an AirPlay speaker, and it will be a good quality one. The secret announcement in September might be that these also act as wireless charging basestations, but that seems increasingly unlikely.