If I put the phrase into Google I find http://thefutureprimaeval.net/postrationalism/ that was written in 2015 as one of the results, so the phrase got used more recently than three years ago.
In general the term isn't important to many of the people that Scott put under that label when he wrote his map. http://www.ribbonfarm.com/ is still alive and well. David Chapman also still writes.
That was my starting point too, but I noticed that most new content linked there specifically about PR seems to have been written pre-2015. If those authors still write, I get the impression that they are not writing about PR anymore.
That makes me suspect that postrationalism was never a 'thing'.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.