I do a lot of WordPress development. Direct FTP is invaluable to me in creating and maintaining these WordPress websites. The FTP client makes uploading plugins and child themes easy.
But the real star in using Direct FTP with WordPress is the online editor. Those of you who work much with WordPress know that editing the style.css file is essential for getting your websites to looking the way you want. Many plugins also have CSS files that may need editing to fit your WP site. Also, there is often a need to tweak various PHP files. The online editor in Direct FTP makes this much easier. The Undo and Redo functions allow me to tweak and test without fear of breaking the website. Undo has saved my bacon on a number of occasions where my PHP tweaks and additions had unintended consequences.
CoffeeCup should take a look at enhancing the online editor in Direct FTP to work more like the your CoffeeCup HTML editor (it's one of my favorites and I'm an editor junky). Enhanced PHP support would also be very welcome. There must be 1,000s of WordPress developers that would purchase Direct FTP just for the online editor. The solid, easy to use, FTP client is just icing on the cake.