Add an official Ad extension
Instead of mid-rolls, why not ad an official ad extension. Maybe this would even be a "free" extension, and not take up a slot. Streamers could decide whether it presents as a chat banner, or a top bottom or side banner and where the ads go on an overlay system. If it's been too long since an ad has played, instead of completely hijacking the stream, banner ads will play where the streamer has opted for them. This way the streamer can ensure that as little important information is covered as possible. If a streamer plays an ad frequently enough, then no banner ad. On top of this, I think that the length of time between ads should be closer to an hour, especially when sometimes ads will then play for several minutes. I take a break ever hour and willingly run ads. If the streamer doesn't activate the extension, then the current ad format will run.