How can I make an off centered niche a focal point?

If there is room, place a table there. If not, a wall piece, picture, sculpture, etc.

Decorative tile or wallpaper would look great inside the niche. You could apply the tile or wallpaper on the wall to the floor to give the entire niche height then trim it out entirely.

How about putting a shallow shelf along the bottom of the niche in a dark stain to ground it. Trim around the outside edge would look good.

How about a shutter effect on each side stained to match the shelf up to where the curve begins.

Don't know what room is to the left but I might tie the colors in with that room since you can see the niche from there.

A few suggestions, just let your imagination run! Have fun, it's a neat spot!

How about a tile mural?

Paint a unique mural. Doesn't have to be big to make an impression.

I would paint a mural

A wall paper mural would be simple

I see it has a light, I might add a metallic like finish to it to give it some glimmer when the lights on. Are you going to put an object in the niche?

I'm with Sharon in regards to the light. How lucky you are to have a light already installed inside! I would install a dimmer control on the switch that goes to this light, and an LED dimmable light bulb. That way you could leave the light on all the time, just varying the intensity according to time of day and season. The eye will always be drawn first to any area that is lit, even a little bit, over an area that is not lit.