Two things that i think def. need to be changed and added respectfully, are :
1) think that when in dip. screen u should be able to demand, techs, gold, cities, etc. without war.. they are red if the ai will not trade, so u cannot demand something if the ai will not trade it with u... this is a little unrealistic, u should be able to demand anything from a civ by threatening war...
2) I would really like to see a mod that makes it possible to say... using spys see what technology a civ is working on, and be able to demand they stop research on it.. this is very realistic in the modern era .. ie nukes , and i think it would be nice to see a mod that makes trading more micro.. i.e. make it so a civ can trade resources but not technologies.. ie technology trading bans.. etc. with the sdk this should be possible, going to look into it ..