I don’t agree. If they combined Dispossessed, free people, ironweld, and any elves, that would become a bloated mess of an army. Also they haven’t done this before like you say. Gitz, BoC, and LoN are not like this at all, they all were once a single army like they are now again. Free people and dwarfs have never been one army, and if elves were included that would put 3 armies together into one.
Also I feel one reason people are up saying we are going to get combined again is that during that interview they said, “Dispossessed would be included and the book itself won’t be called Dispossessed.” Well this is obvious. BoC weren’t called BoC before they got their book, neither were Gitz or LoN. They all had their small respective group names and when put into a battletome they got a new name labeling them all as something new. This will also without question happen to our dwarfs.
If I'm to guess the release for dwarfs will come out later next year most likely, and combine Dispossessed and the dwarf portions of iron weld. Like the fyreslayers we’ll also get some sort of endless spells, along with some sort of terrain piece. At this point I don’t see us getting a DoK style release with a couple new kits, but hey we can still hope for that.