I have a detailed post about this in draft. Something to finish over the weekend !
In general, UDGs appear to have more globular clusters than other galaxies of the same total luminosity, by a factor of nearly 7. These results are consistent with the scenario in which UDGs are failed galaxies: they likely have the halo mass to have formed a large number of globular clusters, but they were quenched before they formed a disk and bulge. Because star formation never got going in UDGs, they are now much dimmer than other galaxies of the same size.
The authors suggest that the next step is to obtain dynamical measurements of the UDGs to determine whether these faint galaxies really do have the halo mass suggested by their large numbers of globulars. Future observations will continue to help us pin down the origin of these dim giants.
On in other words that means this newly-discovered population of galaxies could include significant numbers of giant, almost-dark galaxies. Just how screwed that would leave our theories of galaxy formation depends on the numbers. But AFAIK this method of using the globular clusters to estimate the total mass of galaxies like this has not been well-calibrated, so a high degree of caution is warranted.
http://aasnova.org/2017/07/21/globular-clusters-for-faint-galaxies/
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