Have some ads that don't play sound nor interrupt the stream audio
Automatic mid-roll ads would be much better for the streamer and viewers if there's ads that doesn't interrupt the stream audio content totally, instead just taking most of the screen to display the product/service advertised, with the stream visual being shown in the picture-in-picture. Leaving it as an option (if mid-roll ads have sounds or not) to the streamer would be the best so you could know what the creators want to have on their stream. I know silent ads usually doesn't pays as much as full video ads with sounds, but having less intrusive ads would allow you to play more ads before it's too much for the viewers and have them quit/use an ad blocker.
The current preroll and midroll ads frequently corrupt the audio for Twitch streams on desktop browser.
This forces the user to refresh the page, which loses chat, often repeats the ad, and further delays their arrival to the stream that they wanted to watch. Midrolls made this worse as you could then lose chat mid-stream (very problematic for mods, in particular).
Banner ads with no sound which appear every 30 minutes during a stream for like 20 seconds would be good. Content Creators would need to be able to choose where they show up though, so that they block as little content as possible.
There could also be a warning in the Stream Manager 1 or 2 minutes before the ad shows up with an option to turn it into a full video ad with sound.
And of course, ads need to show up for EVERYONE viewing the stream at the same time.
I think the main concern is that our viewers will go elsewhere or miss out on content if there are ads which interrupt the stream flow. With banner ads, nothing will be missed, so viewers will be more likely to stay.