IceCube-Gen2-Optical is a planned, large-scale upgrade to the existing IceCube Neutrino Observatory. This $\sim$8 cubic kilometer in-ice detector is optimized for point-source science, yielding integer-factor improvements to angular resolution, and increased sensitivity to higher energies. Here, its impact on future study of the diffuse astrophysical spectrum is considered. New analyses of up-going muon neutrino tracks and of all-sky cascade events are performed by adapting standard IceCube selection and analysis methods to this proposed configuration. Improvements to sensitivity of both analyses are presented, along with the combined result. The all-sky cascade analysis excludes a majority of the parameter space allowed by the same period of IceCube observation. The work explores the impact of leading atmospheric systematics on IceCube-Gen2 diffuse sensitivity, and on that of similar, future experiments. A characterization of the Gen2-Optical diffuse program, and implications for our understanding of astrophysical sources in this coming era of next-generation, volumetric neutrino experiments, are provided.