It's not a black swan. The issue is that using Pypy means accepting some potential compatibility hassle, and in return you get a reasonable speedup in your Python code, from glacial to tolerable. But nobody who has accepted glacial speed really needs tolerable speed.

It's like... imagine you ride a bike to most places. But now you want to visit Australia. "No problem, here take this racing bike! It's only a little less comfortable!".

So really it's only of interest to people who have foolishly built their entire business on Python and don't have a choice. The only one I know of is Dropbox. I bet they use Pypy.