> it turns out that there are a lot of situations where PIO can avoid the need for an application-specific peripheral

And I can only repeat: I think that's an aspirational delusion. I'm not aware of anyone shipping a PIO solution to anyone in volume. It's "useful weird" to Hackerspace nerds like us, and that leads to some epistemological skew.

Hardware needs to be boring and reliably supported (by people you can sue!) or else no one will bet a 10k unit PCB run on it. This is anything but.