Hi. I'm in the beta and have to say at the moment Diplomacy is pretty limited. Thats the case with most of the game atm because they are interested in making it pretty stable before they move on to expanding gameplay elements. There is a recent post by Frogboy that says they will take Diplomacy out of the game temporarily for beta 2.
Right now in the game once you have built your first city the technology/research menu's come up. The different technology trees currently available are-Civilization, Warfare, Magic, Adventure, and Diplomacy. The 2 tech trees that are most fleshed out(for testing purposes I believe) are the Civ and Warfare tech tree's. It takesmany, many turns to develop your civilization at the moment.
I do not know the schedule for implementing all of these assets. Currently the techs start out with 3 turns to develop your initial technologies. As you continue to develop techs on the tree they rise in time requirements. Eventually you end up with 20+ to 30+ turns to develop one technology. Also at the moment you can only develop one technology at a time. I don't know if Stardock plans on changing this later to allow for multiple technologies or concurrent training of technologies.
I would say that both Civilization and Warfare Technologies are the farthest along in development(just basing this off the players beta version and not the inhouse Stardock version) with Magic, Adventure and Diplomacy Technologies being very minimal and mostly unusable. The game also allows you to marry someone from one of the quests. After you complete the quest and receive your reward; a popup question follows. It asks if you would like to marry the girl you saved in the quest. If you answer yes, then the girl becomes your wife(instantly at the moment). As time goes on(not too many turns either), you start receiving messages saying you have a baby boy or girl and what would you like to name her/him. These babies then start appearing as full adults within the city that you create. They become heros/heroinnes that you can move and control just like your soverign, champions or other units.
I think the Diplomacy Tech Tree will need to take into account family squables, Feuding families(like Hatfields and McCoys or Yorks vs. Lancasters, etc.) as well as different factions.
Anyways, hope you get enough answers and as always I would recommend checking out Wintersong's stickied post on Elemental: War of Magic for dummies. It is very helpful to new and existing beta testers and game players in general.