I can't remember where I saw/heard it, but I remember someone claiming that Twitter is the world's biggest porn site. It's possible to search Twitter and find pornography, just like you can search it and find people tweeting about video games, their daily lives, etc, etc.
Yet, Twitter is still quoted in the media as a way of measuring public opinion. It retains a sheen of respectability.
I wonder if Twitch are gambling on being able to do the same?
In theory, I don't see why they couldn't - as long as they keep things separate. In practice, I'm not sure if the pornography will become their main revenue and they'll just transition over to becoming something else, following the money. It could get tricky for them if they want to be an ad-supported service and streamers don't label their streams properly.
It's a risky bet to be making, if this ends up changing their image, it'll be hard to come back from.