We develop a boundary-centric framework for black hole physics in which spacetime terminates at an entropy-saturated horizon membrane (HM) that carries all conserved charges and quantum information. Rather than invoking an interior region or singularity, the HM provides a finite, unitary boundary whose formation is triggered when entanglement entropy saturates the Bekenstein– Hawking bound. Adopting a Planck-scale proper-distance cutoff as a working ansatz fixes the otherwise free near-horizon offset scale. We examine the stability constraints imposed by superradiance on any partially reflective boundary in Kerr spacetimes, and derive a benchmark echo-delay scaling implied by the Planck-offset ansatz, alongside an analysis-ready parameterisation that remains agnostic about microphysics. The framework remains exploratory: a full derivation of the membrane microphysics and its connection to fundamental quantum-gravity principles are open problems. If supported by data, this view would replace the classical notion of an indefinitely extendable spacetime with one that is information-limited and self-terminating. This work is part of the CQER-IQ Quantum Gravity research programme. For related research across quantum gravity, cosmology, and information theoretics see: https://cqer-iq.com/