Target Wake Time (TWT) in 802.11ax could actually substantially increase battery life for devices that need to remain connected and can't modem/deep sleep.
Absent a proper 'how to join the local Wi-Fi network' story, IoT connectivity is converging around LoRaWAN anyway.
As I said, I like the 5GHz support, but spinning it as 'power efficient' is a reach.
Just checked & my 2 year+ old APs do support it according to Asus website (Asus RT-AX92U)...so can't be that uncommon
If you buy a battery powered IoT doorbell and it's box claims a battery life of 1 year, but then the battery is dead in a week because your router doesn't support the right 802.11 extensions, are you going to blame the router maker or the doorbell?
Has to start somewhere & seems like good progress
Lots of ZigBee stuff, lots of ESP8266-based WiFi stuff (which generally requires a crummy phone app to perform the initial WiFi setup), and a bit of Insteon stuff hanging on despite whatever the heck is going on with the company.
It’s very much being used! Just might not be that obvious.
Even if you aren't a blockchain fan, Helium[1] is still alive and well. It is helping spread LoraWAN even further. I live in central KY and have several helium networks near me. Never in a million years did I expect blockchain to end up on farms in Central KY, but here we are.
Other WiFi features which allow power savings like APSD (802.11e) have widespread support too.