One thing that annoys me with file navigators - also sadly DO including - is the use of old style disruptive "alert" dialog boxes for one-off error messages.
Eg. consider this when trying to visit an invalid symlink:
User is taken out of context/app flow just for this message.
(in this particular case, choices there are also not that meaningful imho: user could retry by just pressing enter again in original screen, parent and abort have 99% the same effect)
Instead: DOpus could just show a red band on top of the file list in the lister pane. This would show the message, and an X to close it. Any navigation would also close the message (eg in the above case if the user clicks on a now valid symlink)
No disruption, and message is still visible.
I know that this doesn't work well in terms of accessibility/reading software, but it could still be an option to retain the old error alert boxes.