Sources claim Apple is working on "smart home" hardware to work with HomeKit, according to 9to5 Mac. These sources claim that Apple is "beyond the exploratory phase" of hardware development in this area, and believes that smart home hardware could be a mainstream device. Sources also say Apple is likely building a control panel or speaker systems, assisted by the Beats purchase.
Apple Senior VP Craig Federighi Announcing Homekit at WWDC 2014
I think the far more likely scenario is that Apple is going to revise the Apple TV, adding capabilities that make it the "brain" of the HomeKit setup. Virtually everything in my current home setup has a separate piece of hardware that is used to communicate with a controller like an iPhone or iPad. If I could consolidate all of that into the Apple TV which I already use, that would be great.
Seeing as it's more than time for the Apple TV to get an upgrade, nudging sales by having a new model available doesn't sound like a bad idea either. Since the Apple TV already works well with the iPhone and iPad, there's no reason to build a new device. Perhaps a software update to the current model would give limited functionality, but to get all the stuff we saw at the WWDC keynote, you'll need a new one.