While I do agree that Nightly is to some extend "we need crash reports with a list of all the pornhub tabs you had open", I think in this case they should inform users that they are doing this. The study only lasts a week so people can fallback to normal mozilla if they don't like the potential to be the 50% being "tracked".
I hope Mozilla takes this as an opportunity to A) give the networking team a lecture on how to not word a shield study proposal and B) do something to avoid people thinking all shield studies are bad. They aren't.
Because the option C) is "people should learn not to only read the first message in a proposal discussion and assume this is how they will do it" I find it unlikely that it will be possible, given the modern outrage culture in social media.
Wasn’t the famous “Looking Glass” an ad packed as a Shield study and delivered also to Firefox Developer version and even release (not even only Nightly)?
I however don’t expect (and have never expected) Nightly to behave identically as the Release, so I don’t understand that some do expect that, like the OP. The Nightly is your contribution to the development, and obviously its use data aren’t supposed to be “super secret.”