Ultra-diffuse galaxies (UDGs) are spatially extended, low surface brightness stellar systems with regular elliptical-like morphology found in large numbers in galaxy clusters and groups. Studies of the internal dynamics and dark matter content of UDGs have been hampered by their low surface brightnesses. We identified a sample of low-mass early-type post-starburst galaxies, `future UDGs' in the Coma cluster still populated with young stars, which will passively evolve into UDGs in the next 5$-$10 Gyr. We collected deep observations for a sample of low-mass early-type galaxies in the Coma cluster using MMT Binospec, which includes present-day and future UDGs. We derived their dark matter content within a half-light radius (70$-$95%) and total dynamical masses ($M_{200}=5.5\cdot10^9-1.4\cdot10^{11} M_{\odot}$) assuming the Burkert density profile and assess how different proposed evolutionary channels affect dark and visible matter in UDGs. We also discuss observational methodology of present and future UDG studies.