edit: I'll note that if google reader were still around today, its likely the discover algorithm would have been corrupted by bots and trolls and growth seeking managers at google. But back then this hadn't happened yet so it all worked pretty good.
Similar thing happened with XMPP and Google Talk. There was a brief moment in time when you could use any instant messenger with any client of your choice (talk to both Facebook Messenger and Google Talk users via your own server). That also been killed off in favor of proprietary apps.
I'm trying to think of a current-day equivalent of what a shock and disappointment that was, but I'm afraid proprietary protocols and non-interoperable app silos became such a norm that nobody even expects things to work together. I expect GMail to drop IMAP support any day now.