I have some thoughts on diplomacy.

1.A concentrated overview of what relations other factions have between them would be rather nice. Civ IV was pretty good with this, on the one side with the line graph showing either neutral, open passage, vassalage, defense treaty, alliance or war relations. On the other side with the big "at one glance" table. Do I need to post screens what I mean or is it clear?

You could also see the factors impacting their relations. Unless a closer view on faction interrelations was intentionally vague I believe the game could profit from it. At least in Civ IV it really helped me plan my foreign policy. "player x could be potential ally against player y. Isloate player a from player b so that he does not take sides in my upcoming war plans. etc." It's a bit easier to see where it makes sense to put the lever. It is also very interesting to get a view on where conflicts might be brooding (which you can always help along, if it suits your needs ...).

2. I am puzzled that currently there is no trading of e.g. cities or units. Both are usually common, the former for desperate peace settlements, the latter for indirectly waging a war. Also items could be tradeable or maps.

In fact, I noticed that the incentives for trading a bit lower there than elsewhere. The treaties are pretty good, but else? It would be good to have something to give away which does not hurt you losing it. Metal, crystal, horses ... they are all missed somewhat. What about the possibility of trading e.g. those rare resources like wild crops, clay, gold, etc.? Currently, they have mostly local effects, but that could be reworked. If there are a number of them and your realm can only use so much of it, incentives for trading would be much greater. Yes, it goes in the direction of a civ type resources system, which I found a nice addition to foreign policy.

Maybe something could be done with shard usage. (some) common shard use between cooperating factions, with a certain drawback, e.g. less mana output from shards.

3. Another element found in other games: some kind of assembly function. UN or galacic union in other games, where factions can vote on proposals, buy votes and so on. There is an influence mechanism, so a basic function would be there.

4. minor factions. I always liked them in other games. May not fit to the lore.