To me this really looks like a scar from a previous injury. Depending on the horse it takes between 9 and 12 months for the hoof wall to grow from the coronary band down to the ground. So if it was a crack if should definitely look different than it did 8 months ago. I wouldn’t completely ignore it until you know for sure that it’s just a scar, but I don’t think you will have a problem with it opening up and causing problems.
If you end up figuring out it is a crack, putting shoes significantly reduces blood flow to the hoof which delays healing and could perpetuate the problem. I would definitely recommend staying barefoot with timely barefoot trims (which it sounds like you already do that!).