As you know, one great T-shirt design idea can lead to another great idea, and then another great idea, and then . . . So here’s a great idea that you may not want to copy but in an industry always looking for a graphic edge on the competition, it may lead you to another great idea.
I found a 2014 Gizmodo article about this design idea for Tees and bags. It taps into a large market of readers, book clubs, book stores, libraries, and authors.
The Tee or bag depicts a particular book with an all-over print of an excerpt from the book in the background and the image consisting of white space and text.
One way to generate ideas like this one could be to identify a sector of society or an interest group and then think of a design that would appeal to them. People like to be identified with their interest groups and Tees and bags are one way of doing this. There are artists groups, dog clubs, gardening associations, and a host of other interest groups. You already have the technology now all you need is a little research, a little creativity, and some luck to come up with a winner.