I don't see this as a Twitch competitor.
Does it support cams? Does it support streaming from broadcasting software? Does it support archiving recordings? Does it support headset input if the game doesn't have voice support to begin with? The answer to all of these is no and Valve doesn't seem to have plans to add those items either.
What this really is doing is filling a hole that Twitch isn't concerned about: The casual easy stream to my friends/community. I don't know about other's experiences, but my experience with streaming to Twitch casually was a massive pain in the ass. This feature was probably a no-brainer thing to do since it was more than likely just a tweak to their in-home streaming function. So woo-hoo, new feature, not much work required. (Developer mantra.)
Is Twitch concerned about this hole? Probably not. They see it as small potatoes at this point or they would have done something directly to make setting up streaming easier. Also when you have the "professional" streamers who are half game / half talk show drawing in 100-10,000 viewers plus the eSport leagues using their platform for broadcast, they don't care about a casual gamer who may have 0-10 people watching. Even if it's 1000 gamers pulling 0-10 viewers, those aren't sexy numbers for ad sales and that's what drives them.