the thing the Selle Anatomica saddle makers had in mind was a way to make the saddle move with each leg
thats why they separated it in 2 down the middle...

the Brompton saddle adapter pin on top of a common seat post allows a saddle clip to be fixed around it's horizontal tube, above, at slanted angles .
I wouldn't want a saddle which has no fixed position .. might as well not sit down at all ... Note: there are stair stepper bikes already.

But you are welcome to invest in and found a company to make one, and see if it sells on the international market place ..