I don't think that means it's removing unified properties. I think that means that srcElement won't be copied in, but target will still refer to the right thing

I don't think that means it's removing unified properties. I think that means that srcElement won't be copied in, but target will still refer to the right thing (i.e., to srcElement if that's what the current browser is providing). It's just not also providing a copy of srcElement for the user.