It's a grim prediction I make considering my line of work - I foresee people buying/building smaller houses because of the price of oil, and the uncertainty of supply... I dunno if there will be a market for stairs in the years to come...
My knees will not be in the market for stairs in the years to come!
We own another house in Boise which we have been renting that's not built into a hill, and doesn't have 3 levels like this house. It does have an upstairs room, so we do have a stairway.
But it also has a living room ceiling that is too high, IMHO.
The house I am in could never be fitted out for someone in a wheelchair. Too many levels.
A truly energy efficient house has to conform somewhat to a spherical shape, which means that some elevation changes will be necessary. Some of this could be accomplished by making less expensive elevators, which shouldn't be too difficult if designed in from the beginning.
However, if you want to have something that will always be needed, I would bet on windows. The higher tech windows may need to be manufactured in a factory, but the trim is best done on site.