Well I don't know, that's just an assumption. I guess Relic has a deal with twitch and a spectator mode would kind of rival the twitch system.
That depends on what kind of spectator mode we
might get, let's say it's an invite only mode, nothing randoms could join like in DOTA2. I really hope we get something more than implemented spectator maps since the maximum amount of slots on each map is up to 8 players, which would mean that 4vs4 games wouldn't be able to be spectated.
A spectator mode would help the game grow and I hope with all my heart that Relic understands this. People would still be able to stream, not necessarily everone would like to hop in to the game itself all the time.