Structural Plenitude Theory (SPT v1.4) consolidates a unified, relativistic framework in which the physical vacuum is modeled as a viscoelastic substrate (the Pleroma) whose mechanical state governs thermalization, radiative dissipation, and non-gravitational dynamics. This release does not introduce new postulates beyond those established in SPT v1.1–v1.3. Instead, it reorganizes and clarifies the continuum formulation underlying the Structural Flux Paradigm, making explicit the role of: structural coupling efficiency (η), residual radiative dissipation (ℛ), structural impedance (Zₕ), elastic and viscous stress tensors, and causal relaxation dynamics (Israel–Stewart type). SPT v1.4 provides a mathematically coherent substrate-based description in which heat, radiation, and momentum transfer emerge as manifestations of a single structural flux. Classical thermodynamics, electromagnetism, and gravitational dynamics are recovered as limiting cases in the laminar coupling regime (η → 1, Zₕ ≪ Z₍crit₎). The framework integrates and preserves all results from the frozen Zenodo series: SPT v1.1: foundational viscoelastic vacuum formulation, SPT v1.2: phenomenological implications (thermal asymmetries, auroras, refractive effects), SPT v1.3 Parts I–X: Structural Flux Paradigm, residual dissipation, auroral phenomena, comparative structural regimes, and predictive applications to the interstellar object 3I/ATLAS (C/2025 A11). Applications discussed in this work include: planetary latitudinal thermal asymmetries, auroral and polar radio emissions as signatures of residual dissipation, structural regimes in close-in super-Earths and mini-Neptunes, and the interpretation of anti-tail morphology, radio silence, and predicted impedance gradients along the trajectory of 3I/ATLAS. A structured falsifiability programme is presented, outlining observational tests across planetary, interstellar, and exoplanetary environments. Persistent failure of these predictions would directly falsify the substrate dynamics proposed by SPT. This document serves as the v1.4 consolidation layer of the Structural Plenitude Theory, providing a stable, auditable reference suitable for long-term archival, cross-disciplinary evaluation, and future applied extensions (e.g. climate-scale energy audits and atmospheric coupling studies).