Wednesday's release of iOS beta 4.3 to developers brings news of a number of interesting new features (see link below). I was particularly interested in news that iOS 4.3 will allow developers to extend AirPlay support to their own apps. At the moment it is restricted to a select few Apple apps, including iTunes.
Having written about Airfoil and Spotify yesterday, I believe this iOS update indicates that Apple will also relax the rules for Mac sharing of alternative sources (such as Spotify) to devices. However, there is an iOS 4.3 update for Apple TV which supports a broader AirPlay rollout and this in itself is going to be very welcome.