I can think of many application with no need for wireless backhaul, or where wireless becomes a liability. It boils down to cost, power, noise, security, frequency used, and complexity. LoRa or similar is probably better than Wifi for many applications. I like that it isn't opinionated about the wireless stack.

I'm guessing that lots of Picos will see use as enhanced GPIOs for Pi "motherships," which provide backhaul to multiple wired-in Picos.

In fact I have a project which could use a decidedly non-wireless USB GPIO, for use on an airplane imaging system.