I was just thinking that given osx desktop background already has a feature to cycle through a directory of images, if you have imagemagick and curl then to do something that generates backgrounds from online MOTD services could be done in one line of bash.
generate an imagemagick text label at a certain font size, then pipe it to identify -size , pull the width out of that and then use the result to calculate the required font size which you then use in a second textlabel
edit - or just generate a large text label to start with, then scale it to whatever is required
This type of thing would only happen in the OSX app store. It's interesting what a market will pay for depending on where/who you're selling to.