While I have very fond memories of the People Mover, I'm not pining for it to make a comeback. Sometime over the last thirty years or so, the slow little train lost its "futuristic" feel and came to be quaint, retro, and, well, boring. I'm not the only one who thought so, either– there were lots of empty trains toward the end there.
Elon Musk's new Hyperloop design, however, would be an excellent replacement. Take out the old PM tracks, and put in tubes that channel high-speed, solar-powered, air-cushioned pods. Musk is proposing a 720mph route from L.A. to S.F., but a smaller scale would perfectly capture Walt's "transportation of the future" feel. Using clear tubes (instead of Musk's steel design) would add the visible movement Tomorrowland has been missing. It would be an improvement over the Rocket Rods, too- a high-speed thrill ride that still gives a tour of Tomorrowland, but actually works.