I think without drawings it will be hard to get suggestions. Folks will want to see the location and relationship of the arch to the new room. Is the arch inside or outside of the new mudroom?

If the mudroom would become very finished, by that I mean the washer and dryer are behind beautiful cabinetry and the “lockers” look more like a British boot room…then the spaces under and next to the arch could make for an amazing beverage center for the nearby dining room. The drawers or space under the arch could be for special occasion dining storage. You could add lighting in the top of the arch, glass shelf and maybe a great piece of art. I find most homeowners almost never use the front door. How wonderful to have a gorgeous boot or mudroom to enter or leave from daily. Or the spot where the oven is could be for the washer and dryer and the under arch space for beautiful storage of soaps. Depends how you’re going to use the space, what your hobbies are…the brick area could be beautiful as a mini garden bench for flowers or processing produce from you garden. So many gorgeous ways to highlight that area. Good luck and post photos when you’re done!