This is exactly what the OP is asking for. So what, in the thread are you oposing to?
Gnomes have a big faction with it's own culture (house sivis), a nation with a separate culture (Zilargo) and can be found in more mixed cultures like the five nations. Elves have a drangormarked faction, two distinctive nations, three distinctive drow cultures and also can be found in the five nations well integrated. Those are perfect examples of what we are talking about here. Being an elf is the least thing that describes your culture in Eberron. Where that elf is from is waaay more important. Culture/nation/faction first, race second is the way eberron has ever gone.
I'd argue that it's a bit of both. Keith Baker's own blog describes how Elvish minds are truly alien from human ones.
Try reading this blog post about the nature of Elvish, Elves, and Half-elves.
http://keith-baker.com/ifaq-elvish/
In Keith Baker's version of the world, Elves intrinsically known Elvish, as do other Elf-related creatures with Fey Ancestry (such as Half-elves), but if you were a Dwarf somehow raised by a family of Elves you'd have to learn it the hard way. You still might trade Dwarvish for Elvish in your character's Lineage features, but your relationship to the language is different, since Elves are born with the language seared into their brains.
So lineage and culture, in Keith Baker's version of Eberron at least, are two separate layers that should not be confused. Unfortunately, D&D 5e has been bundling the two layers together until now. We can now pull apart the pieces, and the default assumption is that features like basal ASIs and proficiencies (language/skill/tool) are culturally-based while other formerly racial features are lineage-based.
As a side not to this whole discussion, I think there's also a big opportunity to define cultures WITHIN "subraces." The three Drow cultures newly defined are a great example. They'd all share the Elf - Drow features. But they're different domains of the Drow with their own cultures.
Likewise, Sun and Moon Elves are both High Elves (with some Eladrin mixed in) in the FR, while Wood and Wild elves are both Wood Elves in the FR. Gold Dwarves and Shield Dwarves don't fit perfectly into the defined Hill and Mountain dwarf cultures from the 5e PHB, but they're still variations on those lineages, while we've got the 5e Mind-Flayer-enslaved Duergar and the 4e Infernal-pact red-bearded Duergar as great examples of different Grey Dwarf cultures.
We don't need endless varieties of Elves and Dwarves for every environ, but like Humans can have numerous nations and cultures within the already established types. New Elven lineages should not be created unless there's a major reason they can't be reflected in the forms we've already had or can't just have a Prof swap like Aereni and Valenar have in "Eberron: Rising From the Last War."