Has anyone?
My impression is that we have the opposite of a "war" here. These RSS features are dying of natural causes. Unless someone can point me to the conference, blog post, or secret meeting where an evangelist convinced Twitter, Facebook, Apple, Mozilla, et cetera to simultaneously kill this feature in tandem, I'll continue to suspect that they're doing so because they're all subject to the same market pressure: There's a lot of new, popular, paying features that need building, from Twitter and Facebook integration, to mobile apps, to mobile-friendly APIs, to responsive and touch-friendly design, and as these things get added to the backlog other things get pushed down. Code is expensive to maintain and if it doesn't carry its weight it gets cut, even if it's vaguely likeable and nifty.