A feature that would be a nice improvement would be to extend the behaviour of the -f flag to not only grab the keyboard but also draw the window already and start adding entries to the menu as they are received from stdin.
That way, we bring dmenu to the user at the instand t=0, even while a extremely long list of items that would take long to reach EOF is sent to dmenu (sometimes this happens for my dmenu_run script, which cats a history file in addition to the list of executables). I believe there was some mail at some point from someone that was trying to do something like this, but I'm not sure how far did it went. -- Fernando