Dark Elves are my favorite faction, but I recognize the need for the Beastmen to have a serious rework. I'm hoping most dev time goes to them, but I've been brainstorming some ideas for what the dark Elves could get to spice up a new campaign. As it stands, I think that recycling some mechanics from other campaigns could add character to a new dark elf. Here's what I think would be cool and practical:
Legendary Lord: Beastmaster Rakarth
Has his own lore, and his wargear. A solid legendary lord that could feel unique
Rakarth starts on Ulthuan in Tor Dranil or the Shrine of Khaine with a black ark and starting army. His whole deal(and thing missing from the faction as a whole) is slaving other creatures. As such, he would get a mechanic like the Empire has that would give him the opportunity to donate slaves to the major pillars of dark elf society, and if he donated to each of them enough, he'd get a confederation offer from them and a limited time buff. For example, donating to the cult of Khaine could grant him reduced recruitment time/cost forgot sisters of slaughter and witch elves. Donating to the reavers could grant an extra black ark and raiding income, etc.
As a second faction effect, Rakarth himself could get an ability like Yvresses lord capture, but instead of targeting lords, targets fleeing monstrous infantry. After a few turns of torture and replenishment for that squad, that monstrous infantry would get the debuff to stats, upkeep and expendable like Drychas elven units, and could be recruitable to any army. This would help fill a gap in the Dark elf roster while emphasizing slaving. His last faction effect could be to give this capture ability to all his Master heros, master lords, and scourge runner chariots so long as they are in range of black ark support.
Starting on Ulthuan would also give him the opportunity to go fight Norscans(for fimir), to fight Beastmen(minotaurs), lizardmen(kroxigors), wood elves(either Athel Loren or Witchwood(Tree kin), Skaven anywhere(Rat Ogres), or Greenskins(Trolls). Chaos Spawn and undead would not be capturable or recruitable because they are unbreakable or crumble when the necromancer dies, giving a loreful reason for this dark elf faction to want to ally themselves with the tomb Kings, vampire coast, vampire counts or chaos.
It may make sense for them to be able to do the capture ability to some other units, like great eagles, ancient salamanders, feral dinos, manticores or other small single entity monsters.
Last but not least I hope for
New Units for Dark Elves
I'm hoping for Spellthirsters(reskinned magic resistant hydras), a possible Hierotitan-esque Statue of Khaine, and/or Maelithi(ethereal infantry units with frostbite).
As far as Beastmen go, I trust CA to do a good job with their rework, just as they have with the Greenskins, Empire and Brettonian ones.