  The IceCube Neutrino Observatory has recently reported strong evidence for
neutrino emission from the Galactic plane. The signal is consistent with model
predictions of diffuse emission from cosmic ray propagation in the interstellar
medium. However, due to IceCube's limited potential of identifying individual
neutrino sources, it is also feasible that unresolved Galactic sources could
contribute to the signal. We investigate the contribution of this quasi-diffuse
emission and show that the observed Galactic diffuse flux at 100 TeV could be
dominated by hard emission of unresolved sources. Particularly interesting
candidate sources are young massive stellar clusters that have been considered
as cosmic-ray PeVatrons. We examine whether this hypothesis can be tested by
the upcoming KM3NeT detector or the planned future facility IceCube-Gen2 with
about five times the sensitivity of IceCube.
