But I think there is another goal I have not covered:
- The game should make use of other great supplements.
There is a precedent for this, and sadly it has sort of started to die off. OD&D made use of Wilderness Survival to deal with overland travel. This is largely because OD&D was sort of a game cobbled together from other games. In our modern times we really don't see this- game designers don't say "Hey this is a great system for modeling ________, let's just use that!"
I was thinking about economics in Codex and what they should be like, and after some thought and development on RPG economic theory, I realised that I should just use Expeditous Retreat Press' A Magical Medieval Society: Western Europe for population modeling and economics.Because a silver piece could be a days wage in your campaign whereas in mine 30 silver might be a year's income. How much land does the City State of the Invincible Overlord need? This book helps answer all those questions. So rather than trying to create a system that emulates economics badly, why not just say in the book "Check out AMMS:WE by XRP and base your prices and treasure off of that."
Granted this was a supplement for roleplaying, but still, I think it would be awesome if we all started to shill for one another. So from here on out, AMMS:WE is part of Codex.