The closest Dev interaction is this one, when Primal appeared in Daily task as a place to explore.
Come to think of it, it’s might be mostly me who spread this rumors… 
But with more data available right now, I don’t think that’s the case anymore.
Another reason I think Primal is next Overworld Kingdom is its completed background work, but it seems like to be belonged to Primal Rift Faction instead, so no more reason to believe that.
Consider how each hidden kingdom work recently, I didn’t think that would happen.
Hidden kingdom will always be hidden kingdom gameplay-wise, but lore-wise, they will all have one place they belong to: Apocalypse - Sin of Maraj/Guardian - Hall of Guardian/Primal - Primal Rift.
They are like secret faction to that place, but still not actual game’s Factions. Each Factions will likely feature original 4 troops created specifically to work together, not pulling from any existing troops.