This is definitely not unnecessary or impossible, the API is just not at this point yet. There are many cases to consider before this can be implemented.
A channel is not necessarily a simple receiver of ANT+ sensor data (slave channel), it may need to be a master or send/receive ANT-FS data (or any burst implementation).
The manager must allow multiple applications to connect to the same device, and multiple devices of the same type. It also requires raw ANT channels for new profiles or custom implementations.
Some commands can impact the whole radio (ie. event buffering or a reset), and certain configurations (ie. a channel with a quick message period) will have a negative affect on other channels.
The PC implementations currently also have this limitation.