I was culling my stash of old Sky & Tel magazines and ran across this article from 2000 about future telescopes. Here’s how that worked out:
Next Generation Telescope was originally planned for launching in 2009. It’s now called the James Webb Space Telescope, and its launch date is planned for 2018. Two pages over in the magazine, there’s a page titled “Next Generation Space Telescope on the Fast Track.”Giant Segmented Mirror Telescope was planned for “the end of this decade”. It has morphed into the Thirty Meter Telescope, currently being built atop Mauna Kea, Hawaii, next to the Keck Telescopes. However, construction was halted in 2014 by Hawaiian natives on cultural and religious grounds. Prior to the work blockage, the planned completion date was 2022.
Constellation-X Observatory was just a concept, but became the International X-Ray Observatory. That project was cancelled, but revived to become Advanced Telescope for High Energy Astrophysics. Possible launch date is 2028.
Large Aperture Synoptic Survey Telescope was not dated, but construction started in 2014 and is scheduled for completion in 2019.
Terrestrial Planet Finder was scheduled for the “end of this decade,” was planned to be an array of space telescopes for detecting extraterrestrial planets. The project has been deferred indefinitely.
Single-Aperture for InfraRed Observatory is still just a concept.