The more I look at the Campaign/Season/Domain actions idea, the more I think it needs a core set of rules to cover the different actions (to provide balance and represent an extended effort where taking 20 is more common).
I think such a system would need to be integrated into rules for magic item creation, stronghold design, spying, contacts, reputation, advanced animal training rules, apprentice/mentors, statting out communities, family lineage, operating a trading company, long-distance travel, and advanced ruels for craft times. I'm sure there are other things to add to this list...
In this system, I see the four seasons themselves offering certain bonuses to various actions: For example, Winter (season of rest and defeat) would give bonuses to healing grievous wounds but travel is made more difficult. Spring is the time of the harvest, intellectual endeavors are more difficult but simple labor, communal endeavors, and fertility are heightened.
You know, this could be an entire supplement in and of itself!