RSS has a decentralized pub/sub model; the format has been open and stable for a long time; the addressing scheme has no reliance on a specific client. How does the death of one, particularly good even, client, carry with it a threat to the whole ecosystem?
They weren't just "one client" -- they dominated, in the way that MSIE dominated the browser space. And they did what MSIE did, once they gained dominance they froze development (that might have happened through competition) and stopped moving. Everything that was broken in GR became a feature of RSS. And all the things that should have happened, to mature the market, couldn't happen.
Now maybe that's about to change for the better. I hope so. But I'm not encouraged. This is a market where, in order for it to flourish, there HAS to be cooperation among vendors. That's what Twitter proved. Because they control the whole user experience they were able to solve problems that the RSS market couldn't. First, because the vendors wouldn't cooperate, and then because Google took the whole market. So we are now locked into a single vendor -- Twitter.
So the way it looks to me is that there are three possible outcomes:
1. GR's demise is also the end of RSS (which seems to me is Google's desired outcome, based on other things they did).
2. A market develops, but we're unable to get the new features into it that simplify the subscription process, so it has a chance re Twitter.
3. A new dominant reader comes about, and if they're good then maybe something good happens.
I don't think there's the slightest possibility of #3. People in tech are just too insular, they don't study prior art, or even study their competition enough to know where the problems are, much less what the potential solutions are.
I think more likely is a mix between #1 and #2. A continued decline for RSS as an activity and more and more reliance on big companies that don't give a fuck.