Reading all your amazing ideas for a new Dispossessed battletome is great !
Though some things are not "crazy" enough to go with the general direction that Age of Sigmar is going for. For exemple, goat cavalry sounds too much like The Hobbit and classic dwarven designs.
Some mentioned scenery scenes, which sound amazing. It could for exemple help counter some of the Dispossessed weaknesses. A mining/underground scenery which allows a teleport per turn would help compensate our inherent lack of mobility. A giant anvil that helps dispel magic would counter magic-heavy armies.
However, I think that it would be best to leave Dispossessed with these weaknesses, and reinforce our strenghs, thus defining a unique gameplay. What if, for exemple, a unique piece of scenery would be something that forces the enemy to leave their position and come to us ?
Something, like, I don't know... A huge cannon on top of a fortress ? That sounds thematic, crazy AND fun. It could have an area of effect, a very powerful attack, but a minimum attack range. Go under the cannon's sight and you are safe. Thus, the enemy is highly encouraged to rush the strong dwarven defensive lines.
Writing about this reminds me of the (great but now dead) game BattleForge. There were some very Duardin-like fortresses, such as the Worldbreaker Gun, which would fit the bill for Dispossessed I think ->
Or the nameless Fortress, which would be a less crazy and point-heavy investment, for smaller point games ->
Maybe a redesign of the Warriors to make them less vikings and more Duardin. A new type of miners/engineers with a token ranged attack and some utility for other troops ? Or a capacity to "summon" a tower/bunker or other defensive structures on the fly ? Some new buildings and building-oriented units are what would really show Dispossessed as expert craftsmen, imho.