My first attempt at this was not all I hoped it would be, but did prove the concept: I create all the pieces for a t-shirt in Illustrator, add patterns to them, have it digitally printed at Spoonflower, and then cut and sew the garment.
I didn't consult my paper color chips, so didn't realize that the coral color in my shirt would be blaze orange, and I added too many elements. I'm excited about the process, though.
Digital printing, my skills at creating patterns, plus my knowledge of sewing opens up myriad possibilities.