The next stage should be putting them in space. Vibration on earth is a huge problem. Space has a much more stable environment. Also the distance between the laser detectors can be far, greatly enhancing the magnifying power.
In terms of the science, land-based and space-based GW detectors are complementary, as they detect GW waves at very different frequencies. One doesn't replace the other.
There are also serious (if obviously longshot) efforts by colleagues of mine to propose moon-based GW detectors: https://indico.ego-gw.it/event/263/
Isn’t to detect different frequencies it’s a matter of varying the distance between the detectors? Space based detectors can be placed arbitrary close or far, moved at will. Ground based is fixed. Also I remember isolation from Earth’s vibration was a huge if not the biggest engineering challenge. There’s no such problem in space.
