Depends on how it's worked. I'll leave the brainstorming of the implementation to Stardock, but there are certainly multiple variations of a "real" unit. It could be an actual diplomat unit on screen. That could get messy as someone said if you had 20 of them, though depending on how the feature is designed you might never have more than a handful, in which case physical figures are fine.
Why not, each diplomatic unit could used one diplo points like huts use food. And you could use your diplo/prestige points to level up envoys. They learn through diplomacy, but they really "level up" through some thinking about what could made them better, so in an abstract view, by the use of "diplo points" that represents your overall skill and knowledge in that area.
At the beginning of the game, each player can make X number of requests for audience each Y turns. These numbers can be increased by research, however I would suggest keeping the max fairly low to avoid the issues described above, eg diplo spamming, and research sales on a giant scale. Audience (offer/acceptance/decline) and all trades/treaties resolve in the one turn. don't think the complexity of waiting turns to resolve a bargaining set would be fun.
Needs a bit of tweaking, but I like the idea.
First it would be a inightamre to get points that refresh on some defined turns. Instead of that there should be an easy way to know when you will get them back. So a list of envoys on mission and number of turns would let you know exactly when you'll get one point back (or more points if you used more of them)
I like the fact that it could lead to the kind of situation you describe : when you're at war, and short on diplo points you'll have to hold back long enough to try a diplomatic ending to the war.
Let's face it: in most games "diplomacy" is really nothing more than bartering. Sure, I guess you could make the case that giving this for that is a form of diplomacy, but it is a primitive form of diplomacy at best. In the real world, diplomacy can be just as much about shared ideas, goals and mutual respect as it is about immediate gratification. What is more, the idea of diplomatic prestige (i.e., an anonymous flunky versus sending the queen or a duke) is a valid one (just watch a few episodes of The Tudors for some good examples )
It will be hard to create something really new to the kind of things diplomacy can do. Bartering, treaties, one shot help, threatening. What else ? Where Elemental can add some interesting layer is how to use diplomacy. Adding time to do diplomacy would be a good thing. It force the player to really think what he wants : because each time you negociate a pact some time passes. (and let you do some spying to know what diplomacy could give you).
I need gold !
4 turns
OK 50 but I need a unit to defend my city : lend it to me for 40 turns.
4 turns later
Ok but I need 100 gold
4 turns later
no only 75 gold, and you give me the unit
4 turns I can't give you that unit, but if you need help I can cast some nasty spell on your enemy.
Ok we have a deal
4 turns later
Gold is exchanged, spell is cast.
20 turns in total.
A country with a good spying could have proposed at the first time : "you need helkp, I need gold. I hamper you enemies, you give me 100 gold"
4 turns later
Ok but 75 gold
4 turns later
Ok
4 turns later : Done.
12 turns instead of 20.
