Brigham Young was inspired to leave space for elevators in the Salt Lake Temple design
The builders had no idea why, but Brigham Young wanted large spaces, unused spaces in the towers of the Salt Lake Temple and hollow channels running through the granite walls. Years later, the large space was used for installing an elevator and the channels were used for electrical wiring. Was Brigham Young inspired to do this? No, because this legend is not true.
First off, Mormon pioneers were not unaware of the industrial and technological advantages of the nineteenth century. Temple architect, Truman O. Angell Sr. went on a fact-finding mission to England and France in 1856, learning about all technological advances. For example, the Palace of Versailles had an elevator installed in 1743 and a New York department store had a five-story elevator in 1857. In 1837 the telegraph became operational in England and the United States and in 1857, electrical street lights were installed in Lyons, France.
It is true that elevator shafts were not included on the original plans of the temple, but they do show up on the plans as early as 1887. The elevators also take up less than 20 percent of the space in the tower shaft.
As for the channels, work on the walls and floors did not even begin until 1886, a decade after the incandescent lamp and telephone had been in existence. Also, the wiring and pipes were routed through the wood and brick interior structures, not through the granite walls.
For an in depth and interesting read on the construction of the Salt Lake Temple, read "The Salt Lake Temple Infrastructure: Studying it Out in Their Minds" by Paul C. Richards