I believe there is a lot of real estate to be used for ads that is not nearly as disruptive as ones that block out the stream. What if there was an OPT-IN option for affiliates and partners for them to be able to place an "ad panel" into their about section.

This panel would have a few preset sizes (from the most common panel sizes) that the streamer could use and place amongst their other information. It is an area viewers will occasionally look for information, but it would not be blocking the actual content or covering up anything.