I watched an HGTV episode recently where they placed several layers of compound right over the brick; sanding and smoothing in between coats until they achieved the desired surface. They then built a surround with mulitple layers of MDF and built up a molding. Inside the surround they laid out a light colored stone... something like a flagstone. On either side they built white open shelving to house home theater equipment. Sounds a little like what you want. Now... I'm a HUGE fan of glass tile but once you do it... you're kind of married to it due to expense. The beauty of this "spackle" treatment... is you can change out the color, making it an accent wall or blend it in with the existing cabinetry giving it a real built in look. The episode was pretty cool because the chiseled out the stone to create a thick deep enough groove into which they laid tubing through which they ran the all the wires for the home theater equipment. So many ideas out there.....

I think the shiplap and tile sound good but no need for a mantle

If I was looking at this house to buy, I'd want the huge brick blockade below the fireplace to be removed. Edited to add that I see a duplicate post below; you may want to delete that one. Sometimes it takes a while to see a post or reply appear, which is probably why you added this newer one.

Oh, for symmetry, a long vertical art work, or a pair of complementary art works hung vertically on the right to the height of the bookcase top would balance out the bookcase. Or hang several floating ledges in white to display more artwork with top shelf at height of top of bookcase. This fireplace also has a gorgeous frame. (Probably there was a mirror inside that frame at one time. If you had some budget, you could get an antiqued mirror fitted in there. $$$$)