Diplomacy Suggestions

Dark Elves-
Kar Karond war with Marienburg - Interesting experiment/Loreful flavour
Deadwood Sentinels war with Aghol - at least until Norsca DLC, for now they're needed to help hold back the fodder tide from the norscans
Scourge of Khaine war with Avelorn, Chrace, Nagarythe - They took the Phoenix gate and the major city of Nagarythe, but nobody seems to really care, they really should.
Potentially war between Blood Hall Coven and Sentinels of Xeti - considering they're isolated and start hating eachother anyway it might be unneccessary, but I can't imagine the local Slann would be too happy with Dark Elves chilling in Lizardman cities.
Ghrond defensive alliance with Morathi - OK, this is a weird one I know, but hear me out, Morathi is the true ruler of Ghrond. One can assume she's down south for the sole reason of looking for artifacts, I would assume she still has strong connections to Ghrond.

High Elves-
Caledor war with Blue Vipers - Simply to get High Elves involved in central Lustria a bit earlier potentially, plus I've actually seen Blue Vipers go ♥♥♥♥ing ham a few times, maybe this stops that.
Alliance between Saphery and Order of Loremasters - Makes a lot of sense in lore, personally feel AI teclis could use the help too (If they actually bother to send any) also gives Teclis early vision of what the HE's are doing...which makes sense at least in ME.
Saphery starts at war with enemies of Loremasters - only if above is done
Cothique starts with a trade agreement with Reikland - Cothique is very open with over seas trade.

Vampire Counts-
Von Carsteins war with Stirland
Templehof start at war with Ostermark

Skaven-
Clan Spittel war with Tlaxtlan and Xlanhuapec - Spittel were entirely dedicated to hunting Lizardmen, so considering they have so many neighbouring them they should get to it
Septik potentially vassal of Pestilens? - I mean, in lore they are a vassal in the most literal sense, but gameplay wise I'm not sure if it's worth it or even potentially detrimental.

Bretonnia-
Knights of the Flame war with Vampire Coasts - This is to match the undead hunter vibe I went with in terms of Factions Effects
Trade Agreement Between Knights of the Flame and Thegan's Errantry - Fellow Crusaders trading their spoils of war.