Does the superposition principle fail above some mass or complexity?

For a free particle of mass m delocalized over $\Delta x$ for time t, with all known environmental decoherence (gas collisions, thermal photon emission and absorption, light scattering) accounted for, determine whether fringe visibility falls below the quantum prediction, i.e. whether an extra decoherence rate $\Gamma(m,\Delta x)>0$ exists. Progress is measured by the macroscopicity $\mu=\operatorname{log10}(\tau_e/1\,\mathrm{s})$ of Nimmrichter and Hornberger, with $\tau_e$ the largest classicalization time, referred to a single electron, that the experiment excludes for minimal macrorealistic modifications of quantum mechanics.

Interference at increasing $\mu$ with full decoherence budgets that either reveals unexplained loss of visibility or excludes modifications up to everyday-object scales.