Want third-party apps and Siri support? You'll have to pony up for the new Apple TV.
The third-generation Apple TV may be sticking around after today's announcement as a low-cost entry to the Apple TV world, but at a cost: It won't be getting any of the tvOS features shown during today's event.
Apple's comparison page has the two models face off, and the older $69 Apple TV doesn't get Siri, the App Store, or third-party controller support... so, basically, the entirety of the new tvOS platform. Nor is the tvOS beta available for the third-generation Apple TV—only new, developer-kit Apple TVs are welcome.
A large part of this is hardware limitations: The third-generation Apple TV has an A5 processor to the new Apple TV's A8—if the App Store were to be supported, for example, the company would be asking developers to support a chipset from 2012. Do you remember what games and apps looked like in 2012? It'd be a huge handicap limitation, even if the majority of the app were to run on the iPhone and use AirPlay to connect.
This isn't to say that the third-generation Apple TV won't receive ANY software update (with Apple Music goodness) to make it look more like its sibling when the new set top box comes out later this year—I expect that. But if you were hoping to play with tvOS on your existing box, or buy a cheap test unit, you're sadly out of luck.