Stair runner.

overwhelming votes for trend replacement! ouch... that will cost a pretty penny i think. we were trying to stay within budget and stain to match the flooring. in our old house, we had an even more contrasted situation and i didn't mind it - brazilian cherry flooring and red oak stairs. the stairs were stained to match the "red" tones of the flooring and it didn't look bad. is replacing the treads a massive effort? i'm concerned about the wall trim around the treads... and how many rabbit holes we could go down to change them.

We have ~5,600 sf above grade, and a full basement. The third floor was still very much set up to be live in servant's quarters: the 'bedroom' on the left that shows a sink and stove was still a little kitchen designed for the help to use. Our lifestyle does not include live-in help, so we wanted to redo that anyway ;) The servants' stairs were the only access to the third floor- the main stairs don't go up there. Our kitchen-in-four-parts had last been renovated in the 1940s with stainless steel cabinets that found a happy new home with neighbors who have a period-correct house for them! The doors that walled the kitchen area off from the rest of the house literally had different finishes on each side: high end quarter oak floors on the 'family' side of the house, unvarnished pine on the 'servant' side of the house, for example. It was fun to see, but so very impractical for how we use the house these days. Great that you've already investigated what's required- surprises are the worst when undertaking big projects. While a serious undertaking, if you think this addition would be a better use of space for your family and you would include finishes true to the house's heritage... in my book that's worth considering. And while in real life I describe myself as a historical purist, I'm obviously squarely in the 'doesn't deserve to be a steward of a historic house' camp according to many users on this site ;)

Look at the sleeve of the stairs column. Does it look like it was put together like this photo of an ugly stair? The wood treadmill might be screwed on from underneath. Each stair might be just pieces dropped onto the top of the column. If so, you could take off the handrail and then disassemble it. I guarantee it would he a huge pain. I would be tempted to sand as us then stain everything stair related the darkest black solid stain I could find.  It will at least fade into "stair" and not look like you tried to match the new flooring but missed.