Certainly all the travertine would have to come off to achieve your aim. If you had any leftover flooring I would take this opportunity to remove the two wings/ benches. They just seem to be in the way. I guess the best thing would be to find stone that matches the texture and approximate color of existing and then do the German schmear. I think it could work to stucco the lower section from mantle down then have the stone above. I’m assuming you are doing a wood mantle.

Remove what you have on there and for sure that TV has to go somehere else in the space. IMO that whole FP wall area would be arip out it is not nicely designed and once you start removing the stone to replace you might as well redesign that whole area. Olan for the TV on the wall across from the windows to beging this redo.

I would bite the bullet and take the whole thing down. You have beautiful wood windows and a light filled room. The fireplace doesn’t fit at all.

Worth saving your money and redesigning it to complement the room.

I think your fireplace, living room, and kitchen are very pretty. It is really only the top half of the fireplace that is a little bit different. You could actually box that in with drywall and then do another surface, such as paint, contrasting tile, different stone.