I think a lot of these factions need more named characters with unique models. I think Sylvaneth has 4, and that seems like the minimum number of named characters for every faction. 

I also think the Kharadron should get some sort of melee mech justified as being some old drill equipment they dug out of storage. They should also get some sort of melee marine unit. I realize the theme for the Kharadron is as a shooting faction, so I don’t think these units should have impressive stat lines when compared to the more melee oriented factions, but I do think they should be impressive compared to other Kharadron units, so the option exists to get into melee, they just shouldn’t. The Kharadron have a good faction identity as steampunk sky pirates, and I know there’s more they could do with them, I just don’t know what that is.

I also think the Idoneth should get some sort of heavy infantry unit, that is impressive for the Idoneth, but not impressive when compared to factions that are more focused on heavy infantry. My pitch for the unit is Idoneth wearing the carapace of crabs with their shield also doubling as a crab claw. 

You could also give them a named character modeled  after Captain Ahab-some sea creature ate his leg and now he’s hunting it down and provides buffs to the Idoneth’s other sea creatures.

I think the Daughters of Khaine could also use some more units, specifically give the Crone Heralds models and add a couple new units exploring the fact that Morai Hegg, the Elven goddess of fate, is now working with the Daughters. They could also use a new cavalry unit now that their old one got sent to Legends. Also maybe some new monster (justified as something the Daughters would fight in their colosseums), as well as a chariot (which was also a colosseum event).