and tvOS app is not an iOS app, you can't just run an iPhone/iPad app directly on your TV.
it's a completely different interface, Most apps will have to be completely (or at least partially) re-written and re-thought how to interact with it.
i saw a demo of a driving game, which you steer by tilting the remote, just like you steer by your phone. But on the phone, you press the "gas pedal" on the side of your screen, on the TV/ siri remote, you don't have a side of the screen.
it would have to be re-done to integrate the touch surface of the remote.
It will be up to the app developers, in much the same way that some sell universal apps that work on all devices, and some you have to buy twice for both the phone and the iPad.
if Apple allows them to make universal apps that cross the handheld / TV barrier, I can't think of any apps that cross the iOS / Mac app store barrier.