I like this idea.

I have been wondering about why the .... hereos have charisma as it does not seem to do anything (except for the sovereign). This would also (to some degree) justify the passive heroes (researcher, lore master, royalty etc.) if they had slightly higher charisma scores.

Actually this sounds like like Fame in MoM. Capturing cities and such earned you fame while lossing them lost you fame. The more fame you had the more people would approach you to sell you items, heroes looking for work, and so on. The Heroes you had didn't really contribute their stats to your fame score but it was still a global stat that would effect how popular you were.

I like the idea of Charisma bonuses having more of an effect in diplomacy and governance. I think in terms of governance it should be linked to Prestige, ala Cult of Personality. A Sovereign with high charisma should be more likable by other leaders, have more heroes come to work for them, and heroes with high Charisma should improve Troop Moral and having a lot of them should provide a global diplomacy bonus and possibly influence future content in expansions (the mysterious future content, never know what use it may have).

What do you guys think of making reputation and charisma go hand in hand? Right now I think there needs to be more synergy between the various aspects of the game and I can think of a few ways to do this.

1) Make reputation and charisma affect prestige. This will speed up the game a bit and ties those stats to the overall game better and ultimately making them more important. Flavor-wise it makes sense as you would probably take the leader's reputation (and thus the country's reputation) into account before you choose to immigrate there. 

I've also seen talk on the forums about how currently city spam is a problem and people would prefer a "small" number of cities being a viable strategy. This could help that, if you get a sufficient enough reputation boost from questing it would encourage people to focus more on questing and allow a player with high reputation but less cities to have fewer but higher quality cities (because you would have the prestige boost). After all, people's perception of a leader is based on two things, force of personality (charisma) and his/her deeds (reputation).

2) Rather than having charisma as a global skill, as long as reputation is global and reputation works hand in hand with charisma this will be fine. For example, when hiring a champion with another champion he/her should be using their own charisma score. However, reputation should help with that. Flavor-wise again this makes sense as a charismatic person should obviously have an easier time than a less charismatic person. However the kingdom you represent should play a factor. For example if you have two otherwise equal people, you would pay more attention and respect to the one who represents a prestigious organization rather than the other guy who represents an organization you never heard of.

3) I'm digressing here but we need to provide diplomatic options in quests. For example, the early "get rid of darklings in village quest", your options are something like "fighting?.... er i'm more of a diplomat" (you don't fight, quest ends and you get nothing) or "you're not welcome here" (fight the darklings, if you win you get the reward). When I first saw that, silly me chose the first one thinking there would be diplomatic options that would take advantage of my bard sovereign's high charisma. I don't see why can't we have diplomatic solutions to quests like many other rpgs and get experience for doing so. Not only will it make reputation & charisma more important but it would allow for more diverse and viable sovereign builds.