Yeah, that's sort of the market that's picked it up: "I need to connect to old junk". And it would seem like a great fit, except that (as you point out) volumes are tiny and the benefit of a $1 chip vs. a $10 FPGA is high only at scale.

I just checked, and that board is $70. Here's a significantly more capable device with an ESP32 and a iCE40 FPGA which could do the same things and more for $100:

https://groupgets.com/products/ice-v-wireless

I have one and it works great, though not many people picked it up. It's actually available for $50 now, it looks like they're liquidating what they bought.

Point being: is PIO really enabling new solutions in this market? No. At best it's providing a ~30% reduction in retail price for some oddball niche applications. Is that worth the cost of spinning the masks for the chip? IMHO, no.