There is probably no official topic for that, so why not.
Here is complete request from "sticky" Hotkeys / Shortcuts Request List:
- Fit width - Numpad 1
- Fit height - Numpad 3
- Fit width and height ( = fit in) - Numpad 7
- Fit width or height ( = fit over) - Numpad 9
You can use HotkeyP as workaround, but it doesn't work perfect, you can't use hotkey you choose in any XnView dialog, so you shouldn't use Numpad keys.
Here are commands for existing features - first two (other two don't exist, so hotkeys can't be added this way):
Hotkey:
custom, but single hotkeys are not recommended
Command:
Command to active window
Parameters:
176 xnview.exe
Parameters for the other option:
178 xnview.exe
More here:
http://newsgroup.xnview.com/viewtopic.php?t=5661
BTW If you wonder how to get that number (for any option), just press Ctrl+Y in HotkeyP to use "Spy" and perform any action in XnView menu, or context menu.
It should work even better - you could use your hotkey in any dialog, but "Spy" probably doesn't show the same item which is needed as Parameter.