These controllers were all working on SteamOS before as far as I know, so I'm interested to see what this changes. My understanding is that previously their controllers just show up as generic xbox controllers, and now they will be properly recognized. We'll see if this has any other benefits like custom bindings for back buttons and things like that.

Source

Edit:

According to @dualpad@lemmy.zip

got the 8bitdo Ultimate 2 wireless controller with the latest firmware update, and can confirm dinput mode lets me map the back buttons and extra bumpers to different inputs through Steam Input. Analog triggers and gyro work too.