Lightweight, broadband, and highly efficient electromagnetic wave absorbers (EWAs) are increasingly demanded, yet their development remains constrained by conventional equilibrium synthesis, which limits access to the high-energy structural states required for efficient electromagnetic attenuation. Flash Joule Heating (FJH), featuring rapid electrothermal heating followed by instantaneous quenching, provides an effective route to stabilize kinetically trapped structures that are difficult to obtain through traditional processing. This review presents FJH as a platform for non-equilibrium state engineering rather than simply an ultrafast synthesis technique. By interrupting thermodynamic relaxation, FJH preserves metastable phases, abundant defects, fragmented conductive networks, and complex heterointerfaces, thereby creating multiple pathways for electromagnetic energy dissipation. These non-equilibrium characteristics offer promising solutions to persistent challenges in EWAs, including conductivity-impedance imbalance, limited polarization centers, weak interfacial dissipation, and insufficient high-frequency magnetic response. The review further discusses emerging opportunities enabled by FJH, such as kinetic-state programming, structural genome engineering, adaptive electromagnetic materials, AI-assisted materials design, and scalable manufacturing. Finally, the key challenges that remain in achieving predictive and controllable non-equilibrium materials design are outlined. More importantly, FJH is highlighted as a strategy for writing programmable non-equilibrium states, opening new directions for the design of next-generation EWAs.