Basel IV and its practical implications for mid-tier banks

Been trying to get my head around the full scope of Basel IV, specifically how it's actually translating into revised capital requirements and operational changes for mid-sized banks, not just the global systemically important institutions. My firm's in the $50-200B range. Are others seeing significant overhauls to their RWA calculations, or is it more about fine-tuning existing models? What's the biggest practical headache you've encountered in implementation so far?