Depending on what they decide to use as the liquid (some possible liquids won’t reflect as much ultraviolet as visible, and others won’t reflect as much microwave or infrared as visible), the only limiting element would be the detectors they decide to install. Since this won’t be under an atmosphere, it will be able to gather as much or more light than Hubble can (and in all wavelengths as well. Our atmosphere blocks a lot of the infrared and ultraviolet, plus wavelengths farther from the visible). The only drawback to a liquid scope is that you can’t really aim it that well. This will make long-duration observations problematic, if not impossible. Hubble, because it was space-based and a solid mirror, was able to be aimed at one point for very long times, therefore giving us views like the deep-sky survey (the one where they pointed Hubble at an apparently empty section of space, took a very long exposure, and saw several thousand dim galaxies).
