Wow...it's a very interesting game concept, but a question comes naturally to mind: have you already devised out how to implement all of this? I know something about modding, and to me it sounds quite hard to do some of the things you propose, at least not without some very crafty(and possibly annoying) modding tricks. Especially giving some nations bonus gem income from specific provinces/sites, and the whole henges thing, look quite impossible to implement.
Anyway, if you actually know how to do this, I'm definitely tempted to join
About the UW nations, I think that Burnsaber's UWGIM would be a very welcome boost, and you can always cut out specific features you don't like.