We are talking about a situation that will arise if gw brings all Dwarfs into one battletome, so future. And if we talk about future:
Sylvaneth (I'm obsessed with elves, and believe me they are elves just gw makes it a secret 😉), Daughters of Khaine, Idoneth Deepkin, Lumineth Realm-lords, Malerion, Kurnothi. It might turn out that Kurnothi will be implemented in Sylvaneth and Malerion (doubt it) will be merged with Morathi. That's still 4 aelf battletomes vs 1 duardin (if they happen to be merged into one faction). There really is no need for that. Just give some new models for Fyreslayers, like 2 or 3. It will make a big difference to a range that consists of only 3 units (not talking about heroes). Honestly Kharadron Overlords feel complete to me but their theme is so easy to be expended it's a sin not to. I don't know what to do with Dispossessed honestly. I think Cities did pretty well with giving them a second breath. But I know one thing: Fyreslayers and Kharadron Overlords are sooo different, and they both have potential to work on its own that bringing them together will cause more damage than help to them. I've said it before. All factions so far that received combo battletomes are dead in terms of new releases and I understand why. It's easier to support one strong theme like fire berzerkers or steam punk dwarfs than introduce a unit that matches both those themes. It could be done with Orruk Warclans or Skaven but Fyreslayers and Kharadron Overlords? Impossible.