The one you presented in the post I quoted?
That post had a couple of different scenarios. I
think what you meant was how it would work for one lineage to create Drow, Snirfveblin, or other underdark-specific races.
But I'm imagining a lineage that has something like
- 120 ft. darkvision
- cast faerie fire 1/day
- advantage on survival checks in the underdark
- etc.
(Please don't pick that apart for balance/mechanical reasons; it's just an illustrative example.)
So you could play an Elf and take the Elven lineage and have mechanics that everybody (who has played D&D) would recognize as representing elves. But, if you want to play a Drow you would take this lineage, and then just say, "Oh, and I'm a drow elf." So you don't get any of the normal Elven bonuses; instead you get these.
Same thing with a Gnome. Take the Gnomish lineage to get standard gnome-like mechanics, or take this lineage and call yourself a Svirfneblin.
Now, for this to work, you have to let go of some precedent. If you're going to insist that, because the current version of Svirfneblin has "Stone Camouflage", then any future player Svirfneblin race must also have a similar ability. Or, as I mentioned in the original thread, hand crossbow proficiency for Drow. Likewise, you have to let go of "but drow are elves and therefore I if I don't have all those mechanics then it blows my immersion."
I know that for some people this would be completely unacceptable. That if a Drow, for example, doesn't have features X, Y, and Z then it's simply not a drow. In the same way that any attempt at psionics is completely unacceptable because doesn't have features X, Y, and Z.
In the same way that a Dhampir does not have every ability of a vampire.