I know the Black dragonflight is basically extinct, but is just a theory how can be the quest chain for at least Dark Iron dwarves allieds but who knows.
This idea come from be leveling a alt on Highmontain.
Wrathion was saw it in the Embassy of Stormwind (on the Blizzcom beta think) by counterpart for this could be Ebonhorn in the Embassy of Orgrimmar, I think that because both are Black dragons and probably Wrathion can be a way to connect with Dark Iron Dwarves because they live / lived on Blackrock mountain, and basically Wrathion is the only one with some left influence (or strength) there, so I think, he doing this can offers his help to the Allience give then the totally control of Blackrock mountain to the Dwarves (probably the Dark Iron Clan will be please with this), give then a basically a full power forge base for the Alliance army.
Idk if Wrathion or Ebonhorn know of eachother existance but "IF" Wrathion knows probably ask Ebonhorn for his "copperation" but Ebonhorn its secure says something like "dont want to help him because not even being a black dragon he will betrayed his family", and Wrathion probably cannot kill it because his a major character of High mountain clans.
So Ebonhorn for this reason go with Horde to help his relatives of Thunder bluff (Taurens) with the help of Riverbend Tauren Clan, I think his only major help can bring to the Horde be the Knowledge of thousand year dragon as advisor or something for Sylvanas, but he dont give any control to the Horde on High Mountain because for not enlarging the conflictreasons the place stays as neutral (and for be a leveling zone).
I mention the Riverbend Taurens because are the Clan has lost all his land by Dargrull during High Mountain Storyline, but can be of all Clans in general at the end.
I dont mention Wrathion can bring his help advicing Anduin because Greymane and any other Alliance leader will not allow a Black dragon be an Advisor of the king (again).
Possible i been wrong but its just a little theory, any comment or correction is welcome
(dont kill me on hate)
P.D: Sorry for any grammatical mistake.
Edit: BfA (not BoA)