I have both, but I use PI 4 for my current dev environment.
I’ve just checked their website, even the fan hat is out of the stock 
I can create something without the actual device, but I can’t promise it will work properly. I won’t feel comfortable releasing it without even a single test on a physical device.
My idea is to create a service that you will be able to call from any place in Home Assistant.
Something like argon_one.set_fan_speed(20).
This way you can read CPU temp with for example this: HA CPU temps and set fan speed as you like. Even a button to set the fan speed would be possible (https://www.home-assistant.io/lovelace/button/).