Clo - thanks, but FreeCommander supports only lister plugins (for now), I use FC, not TC.
Pierre - thanks for the reply! As I said, it would be useful not just for TC users, but also for the users of freeware file managers now.
Perhaps you could add also some connection with the main XnView program - shortcut to open the image in XnView, similar to Shell Extension.
I tried many other lister plugins, they have lot of advanced features (I don't need), but I miss few basic features (from XnView). I don't need all those advanced feature, just few basic features and mainly navigation features, customizable keyboard and mouse shortcuts (just few).
It would be very useful for me (lots more than Shell extension

), but you have to decide if you want to do it, how complicated and time-consuming it would be for you...
Edit: It could be used also for "quick view" - inside the file manager, not just for internal viewer (F3).