I agree that changing civics is very annoying for larger civs and there definitely needs to be a way to see what's available to you before you repeal your current ones. However, I do not believe a tiered system for civics makes sense. The design of Civilizations in game is to force cooperation to win. Therefore your civic should reflect the current national strategy of your civ. Even if I was playing an all science city, if my Civilization decided to go to war I would understand the need to switch to a civic that hurt science to benifit production.