It seems a little strange to me that we'd have one pretty consistent set of bonuses for backgrounds, and then switch to an entirely different kind for this one. Giving out darkvision also bothers me a little because it's more of a supernatural power; maybe a human from depthworld can see in dim light better (low-light) just from acclimation, but he is still human; he wouldn't be able to see in pitch black no matter how long he lived underground. Scanning the PHB, I don't see any heroic feats that accomplish such a superhuman change. Dragonborn senses is close, and that only grants low-light vision.
To keep things consistent, I'd suggest a background of +1 perception, +4 dungeoneering while nagivigating underground, and no feat chain to follow up on.
If we do want to start adding in feats for regions, I'd prefer we do it all at once rather than piecemeal. So for example:
Citizen of Daunton
Prerequisite: Daunton background
Fluff: Life among the bustling masses of Daunton has honed your social abilities.
Effect: +2 feat bonus to Bluff, Diplomacy, and Intimidate skill checks
Speaker of the Dead
Prerequisite: Valley of Bone background
Fluff: Through continuous contact with the living dead in your homeland, you have become more resistant to the effects of decay.
Effect: You gain 5 resist necrotic and 5 resist psychic. If you already have resistance to either necrotic or psychic, you instead add 5 to that value.
The Kingdom's Discipline
Prerequisite: Kingdom of Jade background
Fluff: Your homeland's military rule and constant vigiliance against demon raids has reinforced your will and sharpened your senses.
Effect: Once per encounter (day?), you may choose to reroll a saving throw that you just failed. In addition, you gain a +2 feat bonus to initiative.
Something like that, I suppose. I'd prefer no background feats at all though; I don't like making house rules unless there's a very good reason.