This comment gave me an idea: what does Trends say for RSS?
It has two results:
- For the search term: https://trends.google.com/trends/explore?date=all&q=rss
- For the "computer file format": https://trends.google.com/trends/explore?date=all&q=%2Fm%2F0...
Both charts are nearly identical.
There's a noticeable blip in March 2013 when the closure was announced, but that blip sits within a concretely downward trend.
I had to dig a bit to locate the very tiny downward slope in July when Reader actually shut down; there's nothing noticeable there.