I still don't think any combined dwarf book makes any sense, but if they did go that route, I think that Fyreslayer and Dispossessed would be the only one that seems plausible. Though it would would seem weird that after all these years, they finally do a full Slayer army only to then refold it back into "regular" dwarfs so soon. But those two at least have some ties to the "old ways" more so than the KOs. Also KO are much more of a brand new army, so I think GW wan't to keep them on their own. Yes, technically Fyreslayers are a whole new army, but even though they didn't bring old models with then(most slayer models being very dated) I still sort of consider them in the same group as Ironjawz, Sylvaneth, and the other factions that took a unit or two from an old world army and was expanded with new models to create a whole new faction.