If they do an update, going back to older concepts probably won't be what happens, nor should it. The only thing they should "go back" to is a unifying theme.
The look of Future World is hodgepodge the way it is. A lot of the great theming of old still shines through, so it wouldn't be hard (relatively speaking) to fix those unnecessarily flourishes (such as when they removed the inappropriate wand) and add appropriate ones. But they do need to give that part of the park a new identity, with the old sensibility. We don't need another attraction named Horizons, World of Motion or Wonders of Life, per se. But we do need attractions that "go back" to being cutting edge designs that teach us something. Maybe we don't need to learn about the history of transportation again, or the development of health sciences. But there are so many other things to look into and examine as an attraction with that old sensibility, that the potential for better concepts is enormous. One person on MiceChat once recommend an Arts pavilion, which sparked all kinds of ideas in my own head. I can't imagine an Imagineer not being inspired by the idea. I once recommended a Space pavilion that focuses on the development of space travel. (Because, let's be honest, that moment when you turn to face the earth on Spaceship Earth is momentous and suggests the totality of effectiveness space would have as a themed ride through.) Something non-sci fi with no cartoon characters worked in for no reason. Energy doesn't have to be twenty minutes of film, and we certainly have ideas about where it's going and what it will one day become. Politics aside.
The only things I can think would actually work if brought back as is would be the iconography (though, icons can and should be refreshed from time to time) and the "Radok Blocks" with an update. There's still nothing quite like those in the real world and twenty years later are still quite amazing.