Huh? AC-4 is just the newest compression. Because the stream can have multiple audio channels, it seems like they're thinking of including different audio sources from the event as different channels and letting the customer choose the mix instead of premixing and sending one stream of audio.

Maybe I'm wrong, but if that's the case, this is as "abusable" as right/left stereo balance.

Anything you're worried about the broadcaster muting or adjusting, they can already do in the mixing booth before it's sent to you.