Observe how well and quickly new engineers come up to speed in your system. What problems do they hit? Think about them while designing. For example what hinder

Observe how well and quickly new engineers come up to speed in your system. What problems do they hit? Think about them while designing. For example what hinders them from solving issues as they come up with customers. Their experience in my view is a representation of the architectural complexity and cognitive load you are inflicting with your design.