I'd love to have ridden Horizons again...we only got to ride it once, not long before it closed. But I got a first-hand example why - it broke down while we were on it, and we were trapped in one of the omnimax dome projection areas where the film kept swooping down on the city...over, and over, and over...for about 20 minutes. Even someone not susceptible to motion sickness was starting to feel it...
(random trivia - those screens now make up the screens in Soarin')
One of this week's WDW Today podcasts mentioned Horizons - either Scopa or Newell I think put out a prediction that Horizons might return in some form in Tomorrowland...but that seemed like a pretty far out prediction...