I fitted structural supports in the wall, behind the plasterboard, adjacent to our stairs, and made sure there was plenty of space at the base of the stairs for the chair to be parked, out of the way, when I designed our house, specifically because I could see a time when one or other of us might need a stairlift. I also fitted very wide doors and flush door thresholds everywhere, to make wheel chair access easier, with clear areas around doors to allow a wheelchair user room to turn and line up with the doors more easily.
This was based on all the hassle we had when I was growing up, with a father that had MS. Our 1930's built house was damned awkward for anyone with a disability and ended up having to be very extensively modified so my father could continue to live in it. We had to build a large extension, with a downstairs bedroom, wheelchair friendly toilet and bathroom and widen most of the doorways downstairs - not easy, as the lintels had to come out to allow wider doors to be fitted. My memories of doing that, plus things like spending a summer holiday building brick walls for raised rose beds, and a wheelchair path alongside it, so he could carry on growing roses, had a fairly big influence on the design of our house and garden.