The SiriKit and HomeKit SDKs will apparently have HomePod APIs. Primary control of the device still has to be done from an iOS device as far as I know.
There's no direct control of the device; i.e. apps are not run directly on the device. Rather, developers leverage SiriKit for a limited set of actions.
By the chosen people, whom have had developmental access bestowed upon them by the grace of Apple.
Seriously though; there is little to no chance that this will not be another locked down device with which Apple will try to monetize your home to the fullest possible extent.
Or: people who paid Apple's $99 developer fee? Hardly a group of "chosen people". This would make sense if you were talking about something like CarPlay, but there's no discrimination here other than the one I mentioned.
Which is the same one that Apple itself uses. This was an issue a couple years ago when Apple kept the fast Nitro rendering engine for itself, but now that they've provided it to everyone else I wouldn't call it anticompetitive.