I fear probability getting this feature is very low because its too specialized or too complicated to add...
In Canon Raw Viewer (Zoombrowser) I can have a mask over the picture, showing all AutoFocus Points, and Highlighting the AutoFocus point that was used for the picture. Very usefull! Please implement that, it needs to be only for Canon

Seriously, if you would implement that, I volunteer to provide you with the correct Autofocus Overlays for each Camera and each Camera Vendor you wish to implement, handdrawn, in any format you need. I think this would make XNview even more special, as I dont know any viewer (aside from the vendors own breeds) who supports that. (For those asking themself why there needs to be a custom for each camera: Afaik, the Autofocus Information is not in X/Y coordinates, instead its just a On/Off flag indicvating if a Focus Point was active or not.)