I am eagerly waiting for beta 3, and I hope to see a more fleshed out diplomacy system. Amongst other games, I think the Civilization series has a great model, which can be good inspiration.

AI is currently ignoring too much information and acting too simplisticly, I think the devs got the message from countless posts already.

The military positive bonus makes it too easy to get high enough relations to be able to make peace with everyone over time. Maybe it does not need to be nerfed, but the AI should be aware of more things so that there can be more minuses to counter the pluses. besides, any diplomacy should be seen simply as a relation of convenience, and can be broken up if the AI ses the gain as better than the loss.

AI should be aware of the second party's relationships with other third parties.

While peace treaties are mostly harmless, other treaties with enemies should count as negative (-1) modifiers to relationship per treaty. I would rightfully be pissed with my ally if it was trading with my enemy, as it makes my enemy stronger. Thus, a trade alliance with an enemy would count as a -1, an alliance another -1, and so on.

There should also be a trustworthiness modifier which would be global i.e. empire A has a single trustworthiness modifier which influences the relations with all other empires. trustworthyness can be positive or negative (or zero, of course). It would build slowly.

I think there should be implicit timers (cooldowns - or warmups, as the case may be) for certain actions. Once a player takes a certain stance, like a peace treaty, he should hold up to it for at least X minutes, or get a negative trustworthiness. Trustworthiness wouldn't wear out over time, it can only be changed by actions. If it goes the opposite way, breaking up alliances, some of them could grant negative trustworthiness.

I think it could have min/max values about -3/+3, but maybe it could work by having the limits as high as -10/+10.

Actions which improve trustworthiness:

Holding up to a treaty/pact for at least X minutes.

Being consistent when cooperating with an empire (small bonus per action like 0.1) e.g. completing successive missions when asked. 

Not attacking ships of a faction you have offered a peace treaty with. You can can defend your gravwells though.

There are no diplomatic missions currently, but  I hope they come up - Stop trading with X, declare war to Y. They have important implications, and should count heavier when building trustworthiness.

Actions which reduce trustworthiness:

Making pacts with mutual enemies i.e. A is trading with B and C, but B and C are at war with each other. A gets a -1 negative trustworthiness for that.

Breaking too many pacts at once. i.e. breaking up a long lasting alliance (first broken pact gets no penalty), and a trade pact (-1), a ship vision pact (-1), a planet vision pact (-1), and declaring war (-1): total -4 trustworthiness in a row. Whenever a pact is broken, there should be a timer of 5-15 minutes; if the player breaks another pact during that time, he gets the penalty.

Backstabbing: breaking a peace treaty with ships already in the enemy's gravwell: -1 per enemy-owned occupied gravwell. Ex.: Say I am a sneaky bastard, and take advantage of a peace treaty to plant 3 starbases on 3 enemy gravwells, to give it a good heat when I attack it. When breaking up the peace treaty, I get a -3 trustworthiness. If I had a fleet on a 4th enemy gravwell, that would be another -1.