Oh, I really like the idea of arming fantasy Kobolds with guns, and other advanced technology!
I've seen some fantasy settings give Goblins a sort of fanatical and savage lunacy niche, with Pathfnder for example making Goblins extremely superstitious about writing, suicidally insane, and obsessed with fire and so on, while other settings try to give Goblins a technological angle with robots, guns, and so on, with Eberon (iirc) making Goblins a fallen technologically-advanced empire.
But, now that you mention it, Kobolds seem to me a more appropriate fantasy creature to get a "lost technology" angle: a sort of primordial humanoid creature whose time has been and gone, driven into the underworld by catastrophe, replaced by warm-blooded creatures, and left to bide their time away in shadows for the stars to come around right for their return, as they are dwarfed and stunted by theri long imprisonment in the hollow earth.
Draw some inspiration from Lovecraft's "The Nameless City" for the default fantasy Kobold:
I saw that the passage was a long one, so floundered ahead rapidly in a creeping run that would have seemed horrible had any eye watched me in the blackness; crossing from side to side occasionally to feel of my surroundings and be sure the walls and rows of cases still stretched on. Man is so used to thinking visually that I almost forgot the darkness and pictured the endless corridor of wood and glass in its low-studded monotony as though I saw it. And then in a moment of indescribable emotion I did see it.
Just when my fancy merged into real sight I cannot tell; but there came a gradual glow ahead, and all at once I knew that I saw the dim outlines of the corridor and the cases, revealed by some unknown subterranean phosphorescence. For a little while all was exactly as I had imagined it, since the glow was very faint; but as I mechanically kept on stumbling ahead into the stronger light I realised that my fancy had been but feeble. This hall was no relic of crudity like the temples in the city above, but a monument of the most magnificent and exotic art. Rich, vivid, and daringly fantastic designs and pictures formed a continuous scheme of mural painting whose lines and colours were beyond description. The cases were of a strange golden wood, with fronts of exquisite glass, and contained the mummified forms of creatures outreaching in grotesqueness the most chaotic dreams of man.
To convey any idea of these monstrosities is impossible. They were of the reptile kind, with body lines suggesting sometimes the crocodile, sometimes the seal, but more often nothing of which either the naturalist or the palaeontologist ever heard. In size they approximated a small man, and their fore legs bore delicate and evidently flexible feet curiously like human hands and fingers. But strangest of all were their heads, which presented a contour violating all known biological principles. To nothing can such things be well compared—in one flash I thought of comparisons as varied as the cat, the bulldog, the mythic Satyr, and the human being. Not Jove himself had so colossal and protuberant a forehead, yet the horns and the noselessness and the alligator-like jaw placed the things outside all established categories. I debated for a time on the reality of the mummies, half suspecting they were artificial idols; but soon decided they were indeed some palaeogean species which had lived when the nameless city was alive. To crown their grotesqueness, most of them were gorgeously enrobed in the costliest of fabrics, and lavishly laden with ornaments of gold, jewels, and unknown shining metals.
- HPL, "The Nameless City"
I would kind of think of the Kobolds as the real brains of a lizard-man empire: diminutive, weak, spindly, pale, decadent, and sensitive to the light of the surface world, but infintely old, wise, wicked, clever, and jealous of those warm-blooded things that have inherited the sunlit world of the upper surface, sending out tribes of larger, less sophisticated, more brutish Lizard Men to do most of their dirty work for them by day, while the Kobold sorceror-king taskmasters work subtler mischief by the light of the moon, using strange weapons and even stranger machinery crafted deep in the earth's shadows in the Kobold's weird workshops and laboratories....