I think the gatehouse is the most likely place we will find a cave goblin maiden, the problem will be finding the key and gaining access.The higher level of the fort is where the locked main door is. It's still the Cave Goblin stronghold, it's just MC & the Giantesses never go up they just escape through another cave entrance.
I think if we get a Cave Goblin update it will remain in the Goblin Valley area like all other Goblin Arcs. Perhaps mining beneath the Hall will lead MC into conflict with Cave Goblins that way.
I can't imagine any number of cave goblins will present much of a challenge unless a new, more deadly, element is introduced into the game.
Crown of sorcery, crystal egg, lightning strikes and familiar in tow with fire are an unbeatable combination at the moment.