RSS/Atom feeds are fading - at least for now. Twitter stopped providing them years ago. Google Reader Social had them, G+ does not. Facebook removed personal page feeds. Tumblr barely provides any.
On the other hand, subscription/notification is ubiquitous. It's just all proprietary.
I assumed this was due to business issues; a desire to lock in customers.
Perhaps there are technical issues that contribute however. Is Atom/RSS fundamentally and unfixable flawed?
