A typical elevator/lift is about 6x8 feet, so a single elevator shaft could carry three or more 2x4 elevators, just right for the single rider or couple that typically travel together. This would speed riders on their way with reduced wait time and cost no more, since the additional mechanicals would
also be smaller and cheaper.
But heres the thing: I find I often need to use a restroom on my way to or from a meeting or lunch, and I often need to take an elevator to get to that meeting or lunch. As long as people often need to visit both, and theyre often in the same vicinity, and were building the elevators the size of restroom stalls anyway, we might as well install toilets in them. [link to illustration]
Not only would it save a few minutes of travel & restroom time, but it has the added advantage of allowing us to convert most restroom space to personal elevator toilets as well. And well need the extra elevators since some people take a while.
The mechanics are tricky, but not impossible. Fresh water would be fed in thru a flexible hose. After flushing, the sewage would fall thru a telescoping pipe into the sewage system in the basement or perhaps be held in a tank hanging under the cab for automatic transfer later. You can wash your hands in a little sink mounted above the toilet and check your look in the mirrored surface of the door before unlocking and exiting.
This scheme would eliminate embarrassing elevator farting *and* the common fear of being trapped in an elevator and having to go to the bathroom. (This is common, right? Its not just me?)
This would not eliminate the need for a service elevator, of course, since large carts, wheelchairs, emergency stretchers, enormously fat people, and taxidermied swordfish wouldnt fit in the personal elevators, toilet or no toilet.