Having spectators requires the bandwidth of another player being in the game, and actually a bit more since the spectator is going to need faster updates.
So if you have a 4v4 match, allowing 8 spectators = a BTB game.
Why would you allow 8 spectators? Why would you even need it to work over the internet? One over LAN would suffice for MLG. Just make it a monitor that can't affect the game. They could always just switch the feed for first person mode.
But I guess this is a highly specific use case that would probably not be worth time and money to invest.