It may not matter if SmartThings supports HomeKit or not. One way to look at HomeKit is that it is a UI superstructure with good iOS 8 support, including fairly deep Siri integration. The SmartThings hub will be a “bridge” in HomeKit. Just as developers have already implemented UI superstructures for ST, e.g. ActiON, Home Automation Dashboard, etc., a developer other than SmartThings can do the same thing with HomeKit. If ActiON can scarf up all of your devices into a Dashboard, a similar app could scarf up all of your devices into HomeKit. The cool thing about a HomeKit bridge, is that while the bridge device (ST Hub) handles all of the “dirty work” of running the devices (think Z-Wave and Zigbee), those devices show up in HomeKit in Homes, Rooms, and Accessories. This should be pretty straight forward, and it should happen with or without ST involvement. If ST has a problem with Apple’s terms, one of us as a developer probably would not have the same problem.
I don’t think HomeKit is such a big deal, unless you really need Siri for some reason. I sure don’t walk around my home with my iPhone, just hankering to tell Siri to turn on a light. Interesting issue is that HomeKit only works when the iPhone has connectivity, just like ST only works when the hub has connectivity. It’s fairly obvious that robust HA requires at a minimum a hub like ST’s to function, and HomeKit doesn’t address that need AT ALL. It makes an accommodation for it through it’s bridge support and functionality, but someone else has to provide the hub.