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.

That sounds like a fun experiment :) I can confirm that people are willing to pay for simple apps that has a positive impact on their life.

How would you solve choosing the right font size though? It should be such that the longest line perfectly fits the width.

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