In my experience even sending hundreds of thousands of resources doesn't get you anything.

The only way diplomacy 'works' is seeking a ceasefire upon first contact in the early game. If you get cease fires then you can eventually get shared vision and a full alliance over time from one of those players. But even that is temporary. In the final stages on an 8 player map, my ally broke the alliance to stab me in the back despite being vastly weaker. Why? I've no clue - it was suicidal! All it meant was I had to delay my conquest of the enemies' remaining planet or two to crush the dozen or so worlds my 'ally' had.

It's something that probably deserves a total revamp at some point, but maybe it works fine for PvP? For PvE, something that tracks reputation i.e. how many cease fires etc have you broken, sentiment i.e. how many missions have you completed for a player, how many resources have you given them, how many of their enemies' ships or worlds have you destroyed, who is allied with whom, that sort of thing, would be good.

Vasari Alliance already get Advent Shield Burst via Reverse Engineered Shields, a Tier 3 tech that grants +15% Max Shield Points, as well as +15% Shield Regeneration albeit at a cost - regenerative shielding is interfered with while the burst is charging. They also get a TEC armour upgrade - Armour Restoration at Tier 4 which grants +15 Armour Strength and +15% Max Armour Points.

Hybrid faction ships and the like would certainly be interesting. What might an Alliance-Enclave titan look like? Hopefully better than the flying brolly! (Umbrella)

Something showing disposition between factions, and causes of recent changes would be interesting, but I'd suggest one modification - known changes v unknown. If you haven't met a faction then you can't track changes. And even if you have diplomatic relations, maybe you need a diplomatic or spy ship or appropriate relations to track that info?

War crimes should be subjective. Stripping your own unpopulated planet shouldn't be an issue. Seizing an enemy populated planet then imploding it however ...   Is there really a difference in how you wipe out enemy control of a planet though? 

I guess I'd be thinking something along the lines of Civilisation - not sure what the latest versions are like, or the Total War series - again not sure latest versions.

The big question is, is this a direction the developers want to go? Limited diplomacy is fine for PvP, it's really more a PvE matter. Now if there's a campaign of sorts then diplomacy might be more important?

We still don't know what the 4th faction will be - I'm interested to see what they do and if they pull it off. We still technically don't even know that it's the faction chasing the Vasari and wiping out everything. It could be another alien race - Vasari but not, a returning race of sorts - something that used to live in TEC space but has now woken up or returned, the 'Big Bad' or something else, depending on the creativity of the developers. In some ways keeping the Unknown as a nebulous ever lurking threat could work out better. Or, they could include a facet of the threat, but make clear it's not the real threat, unrelated footsoldiers, conscripts, or mindwiped slaves depending on the possible nature of said threat.