Digging your own (small) caves sounds alright, but I don't think cave folk should be accomodated much more than they became with the recent update. Let's face it, there are already too many advantages.
-No decay
-Building materials for palisade/brickwall reduced drastically
-Someone would have to build/protect a battering ram outside of the cave and then inside of the cave, then navigate their way through the long cave to find where the village is hidden only to have to build yet another ram... Pretty much impossible to siege unless they bring a large group of people carrying building materials, perhaps accompanied by another group to defend them since the first group wouldn't have room for arrows and stones from stalagmites are useless with the sling nerf
-No drive by murders
-Ease of access for mining
-Ease of access for cheese making
-Don't have to worry about boars or bears (if you're too weak to kill them or don't want to be interrupted when you're just running errands)
Disadvantage: You have to spent a small amount of travel weariness to get out of the cave whenever you need materials.