Given that the folder compare feature gives message “not yet implemented” since a very long time, I am asking you to implement this quick workaround, while waiting for an embedded implementaion.
In the preferences, allow the user to specity the full path to an external file comparer executable.
Then, with the ‘compare dirs’ you just invoke that executable passing along two arguments, the left ad right panes directories.
Similarly, the same mechanism for two currently selected files, one on each pane, should also be very useful.
Similar tags should also be available in the command row, otherwise it is pretty useless.
For example, %1% should expand to the left pane path and so on. Also the expanded list of selected files would be very useful, if made available on a given tag.
At the very least, this latter feature would save the day, and maybe it’d be easier for you to implement. The former would be better, of course.