That almost looks like grain runout, where there was some curvature in the grain pattern, but the wood was flat sawn to make a guitar back. The end grain did not take the stain the same way as the other parts of the wood. The other possibility is that this is pore filler that has somehow changed color or rejected the stain. Either way, it would be prudent to get an opinion from your dealer or from Taylor directly before making a final decision.
Taylor can probably help your dealer locate another example in stock somewhere. They've done that before. I understand that you paid for new and want your baby to be perfect, but this may be a case of learning to live with it if you are otherwise very happy with playability and tone. Remember that you look at the upper side and the front a lot more than you see the back. Worst case, it has to go back to the mothership for correction and refinishing, under warranty of course.
