The next generation of ground-based telescopes will give access to resolved stellar populations in previously unexplored environments. To highlight the potential for stellar spectroscopy using an extremely large telescope (ELT), we present data from an ongoing project with the Very Large Telescope (VLT) to calibrate a novel method of distance determination. An ELT would extend the reach of this method and would allow quantitative studies of individual stars well beyond the Local Group, sampling a wide range of galaxy morphologies and metallicities.