For example I expect exo-mount -v to display version information even when there is no display, instead of printing "exo-mount: cannot open display:". But essentially, I'd like exo-* commands not to fail when I use the --no-ui option and the display could'nt be opened. Although I understand it's important to return as soon as possible when the UI could be needed.
Xfce is assumed to run under an X session. All the application in Xfce/Exo that initialize gtk (and thus fail when no display is available), use error dialogs or other widgets, so the rare case you use this to just print a version will add a lot of code and make the whole thing a lot more complex.