When things dont go as plan we just need to improvise. There is no way to guarantee that if you even change all wood planks this kind of thing would not happen again over time. A metal strip at your choice of metal can be made an intentionally decorative item. Just insert it to fill the gap. It could even give you an interesting contrast to the wall.
I had a very similar thought with an unvoiced suggestion in his WaxRax thread. Which was exploring, I did a quick websearch around LB to no avail, the availability of semi-modular custom built industrial shelving of the sort one might find in a specialist library or executive storage system. Embellishment might not be to his taste. Storage or wall improvisation in the preferred wood. Your comment was in any case quite in line with my thoughts.