There are different types of interferometry and different "waves" of interferometry development. The first wave started around the mid 19th century and saw the

There are different types of interferometry and different "waves" of interferometry development. The first wave started around the mid 19th century and saw the advent of lots of new instrumentation that revolutionized science. Speed of light measurements. The Michelson-Morley interferometry test which laid the foundation for Relativity. Later FT-IR instrumentation. Fabry-Perot imaging. Etc. The second(?) wave happened in the late 20th/early 21st century and surrounded visible light imaging, synthetic aperture interferometric telescope systems. Most major large telescope installations built since the 1990s have incorporated interferometric plans into them. The Keck 1 & 2 telescopes, for example, and the Very Large Telescope array. Both were built with the idea that interferometry systems would enable observations with "virtual" telescopes having diameters on the order of 100m. However, that hasn't worked out to be nearly as useful nor as practical as was imagined. The Keck Interferometer has been mothballed due to lack of interest/funding and the VLTI has been rarely used and has struggled to remain relevant. In fact, it's been found that large telescopes aren't particularly advantageous for interferometric unit telescopes. Add to that the saga of space based interferometeric observatories, which have so far come to naught. There was the long-planned, long-revised space interferometry mission which was finally cancelled some years back. Then there were several varieties of telescopic interferometer arrays or formation flying fleets tasked mostly with detecting and observing distant planets (such as NASA's "terrestrial planet finder" concept and ESA's "Darwin" concept along similar lines). The idea of those was to use interferometry to both create very high resolution imaging and also to deeply "null" the starlight of parent stars. Over the last decade or two the limitations and difficulties of interferometry have become more apparent and the competitive advantage of alternate methods (such as large ground based telescopes using ordinary coronographs coupled with adaptive optics and space-based telescopes using coronographs) has more or less erased the promised future of interferometric telescope arrays as a new major class of instrumentation that would open up huge new realms of observation.