Opting in and out would be great. Of course, it would be a battle between developers. I think buyers like the info, but anyone who wanted to keep their earnings secret would feel very pressured to give up the info.
Most of us are on the other side and want to know, however, I can see where someone who created an app and told family and friends would not want them knowing how the app is doing ("Hey, you buy the beer big shot!").