  The evidence for dark matter particles, $\chi$, is compelling based on
Galactic to cosmological scale observations. Thus far, the promising weakly
interacting massive particle scenario have eluded detection, motivating
alternative models of dark matter. We consider scenarios involving superheavy
dark matter (SHDM) that potentially can decay or annihilate to neutrinos and
antineutrinos. In the mass range $m_\chi=10^7-10^{15}\,{\rm GeV}$, we evaluate
the sensitivities of future observatories POEMMA and GRAND for indirect dark
matter detection via the measurement of neutrino-induced extensive air showers
(EAS), compute the Auger and ANITA limits using their last up-to-date
sensitivities, and compare them with IceCube limits. We also show that the
uncertainties related to the dark matter distribution in the Galactic halo have
a large impact on the neutrino flux. We show that a ground-based radio detector
such as GRAND can achieve high sensitivities due to its large effective area
and high duty cycle. Space-based Cherenkov detectors such as POEMMA that
measure the EAS optical Cherenkov signal have the advantage of full-sky
coverage and rapid slewing, enabling an optimized SHDM observation strategy
focusing on the Galactic Center. We show that increasing the field of view of
the Cherenkov detectors can significantly enhance the sensitivity. Moreover,
POEMMA's fluorescence observation mode that measures EAS above $20\,$EeV will
achieve state-of-the-art sensitivity to SHDM properties at the highest mass
scales.
