  The Event Horizon Telescope has produced resolved images of the supermassive
black holes Sgr A* and M87*, which present the largest shadows on the sky. In
the next decade, technological improvements and extensions to the array will
enable access to a greater number of sources, unlocking studies of a larger
population of supermassive black holes through direct imaging. In this paper,
we identify 12 of the most promising sources beyond Sgr A* and M87* based on
their angular size and millimeter flux density. For each of these sources, we
make theoretical predictions for their observable properties by ray tracing
general relativistic magnetohydrodynamic models appropriately scaled to each
target's mass, distance, and flux density. We predict that these sources would
have somewhat higher Eddington ratios than M87*, which may result in larger
optical and Faraday depths than previous EHT targets. Despite this, we find
that visibility amplitude size constraints can plausibly recover masses within
a factor of 2, although the unknown jet contribution remains a significant
uncertainty. We find that the linearly polarized structure evolves
substantially with Eddington ratio, with greater evolution at larger
inclinations, complicating potential spin inferences for inclined sources. We
discuss the importance of 345 GHz observations, milli-Jansky baseline
sensitivity, and independent inclination constraints for future observations
with upgrades to the Event Horizon Telescope (EHT) through ground updates with
the next-generation EHT (ngEHT) program and extensions to space through the
Black Hole Explorer (BHEX).
