I just implemented this format in my game engine and the performances are crazy: images loading is 3.2 times faster (compared to png) and 40 times faster to generate game screenshot!
The generated screenshots are lighter (about 5%). However, the resource images in QOI format that I load are in average a little bigger (about 5% and sometimes until 35%). I guess it is not the perfect solution for AAA games which already use more than 30go nowadays.
"AAA games" (or rather any 3D games) typically use lossy image file formats which directly map to the hardware-compressed GPU texture formats (like DXTx/BCx in DDS or KTX containers), QOI is an interesting alternative where lossy formats don't work well though (e.g. pixel art).