Distance from ΛCDM in σ (left) and DETF FoM (right) as a function of the assumed zero-point calibration prior and gray dispersion—the two dominant systematics most likely to improve in the near future. Values in parentheses correspond to forecasts without a separate sample of new low-z SN. The 5σ threshold is reached or exceeded across a wide range of assumed priors. Neither systematic alone drives the final constraints.