I would put your electronics for the tv hidden in the box and place TV flush with wall. There is an outlet there. You would have to place a wall mount that would reach out enough for Tv to be flush with outside wall.

Since there is a spot light above I'd think about placing a piece of sculpture here. Another approach would be to place a large Amethyst crystal geode or quartz specimen on a stand. When it's lit it would bounce the light around and make for a striking conversation piece. Coral (red or black) will also be cool.
I'd also think of the entire space as a whole composition. So, to the left of the niche hang a single photograph or print. Have the print and what you place in the niche relate. If you use a piece of sculpture, a photo of a similar subject will work well. If use go with a natural element like a large seashell, hang a photo or print of the ocean or beach. Is there some other location for the TV? It's going to give you a stiff neck if you put it above the FP.
Jeffrey Brooks Interior Design

I was also wanting to mount the tv but gave up the plan thinking it will be too costly for getting that done and its a rental place for which I would move out in a couple of years. Why shell out money for a temp solution was my thought