This is a really great quilt and I am glad that you were able to re-size it to meet your desired size. Stitching in the ditch would be great but will be difficult unless you do it FMQ style because of all the corners and you don't want lots and lots of starts and stops. I have been looking at modern quilts with admiration lately because they are so totally different. I have noticed that lots of the quilting is straight line, close together and modular. Might these fit your concept. I think they would be easy to do. Perhaps you could make a sample block and give it a try. You can also draw them on a translucent paper and audition them on your quilt.