I'd say at least half the factions have at least some extra units, there are certainly a lot of extras overall, though Wood Elves, Skaven, Beastmen and Lizardmen have received the most work. Off the top of my head, Tomb Kings, Undead, Chaos Dwarfs, High Elves, Dark Elves, Araby, Kislev, Brettonia have all had at least one addition apiece. I'm hoping Empire and Dwarfs will get additions too but I'm waiting on a couple of modellers there. There are a lot more area-specific rebels and mercs too, particularly in areas like Marienburg, Estalia, Ind or Albion that narrowly missed the cut in terms of us being able to fit them in as actual factions.