Software-Defined Vehicles ( SDVs ) leverage Over-The-Air ( OTA ) update to continuously provide users with a diverse range of services and an enhanced experience. However, this software-centric approach introduces a dynamic landscape of cybersecurity threats alongside its conveniences. Traditional Electronic Control Unit ( ECU ) system design struggle against the evolving demands of SDV. To support rapid software changing, we must reconsider automotive ECU design philosophy. So, which traditional cybersecurity design principles are being challenged? Which remain essential? This presentation will share practical experiences in ECU cybersecurity functional design, exploring the challenges to embracing the era of SDV.