We review the design motivations, technological challenges, and recent progress toward a highly granular silicon-tungsten electromagnetic calorimeter (SiW-ECAL) suited for future lepton-collider detectors, such as a Higgs factory. We describe ongoing developments -- ranging from compact embedded readout electronics to test-beam campaigns -- and how these efforts address the stringent requirements of future detectors. Finally, we discuss design optimisations and the roadmap toward a full-scale ECAL system.