I've noticed when some ads play they take over the screen and the stream is moved to be above the chat until the ad ends. I think this should be reversed. Ads should take up that space above chat and then disappear; or, perhaps, they appear in the corner of the stream. If this were done, of course, ads would likely have be silent -- and I doubt any user would be against that.
Whatever the case, ads taking up the entirety of a livestream is just not acceptable and advertisers/Twitch need to figure out a better way to have ads without them being absolutely intrusive on the experience. Imagine you go to a live event and then for 10-30 seconds, your entire vision is blocked out: you can't see or hear anyone/anything except the ad. That's what it's tantamount to.