Ensuring the safety and reliability of Cyber-Physical Systems (CPS) is critical, particularly in safety-critical domains such as automotive and aerospace. Fault Injection (FI) is a well-established technique for testing system resilience, but current FI tools often face challenges when applied to Simulink-based CPS models. In this paper, we analyze the shortcomings of existing FI methods, and reflect on the key challenges of FI for Simulink-based CPS models. By offering insights into these challenges and proposing research pathways, we aim to inspire further advances in FI methodologies, enabling more robust testing of CPS in real-world applications.