I expressed it poorly.
I get that there are other factors in play that shape a society and define its culture. I'm not asking "how do I make people from Breland feel distinct from people from Karrnath?", or "how do I make people from rural Breland feel different from city-slickers in Sharn?", or even "how do I make a well off Sharn socialite different from a impoverished daylaborer from the lower parts of the city?"
What I'm asking is, what distinguishes two individual characters who share the same cultural background from one another when the only meaningful difference between them is that one is human and the other Khoravar? How does the choice to make this character a Khoravar instead of a human change who and what they are, independent of other factors? Previously, that had answer - not a huge one, to be sure, but an answer nonetheless. Now the answer is "nothing, unless you go all in on the elven side of the Khoravar's ancestry", which isn't an answer so much as changing the question to "what makes an elf and a Khoravar different?" instead.
Species is a building block, one of many used to piece together both individual characters and entire societies, and the rules that the playtest currently proposes say that it's a building block that mixed-ancestry people do not get to work with beyond picking which one of their parent species they "really" represent - no matter how many generations removed those "parent species" might be.
As a minor example, albeit homebrew: Keith Baker has floated the idea that the Elven language in Eberron is innately magical in nature and that those of elven descent simply know how to speak it instinctually without needing to be taught, even automatically updating with new vocabulary as its native speakers encounter new ideas and technologies the language didn't previously have words for. Because this is fundamentally the consequence of the elven peoples' fey origins, this gift is passed through their Fey Ancestry trait, meaning that previously, all Khoravar (i.e. people of mixed human and elven lineage) could be expected to be able to speak it, because they all had the Fey Ancestry trait by virtue of their species. Humans and other non-native speakers have to learn the language as normal, and don't benefit from new vocabulary updates automatically downloading into their brain whenever an elf halfway across the world needs a word for something that has never been expressed in their language before.
With "Pick a Parent" being the way mixed-ancestry characters are assumed to be handled going forward, the assumption that Khoravar gain literally anything from the mechanical kit of the elven side of their lineage is now an all-or-nothing proposition. Want Fey Ancestry? It's now stapled to Trance, a cantrip and a couple of spells, and an elven lineage choice that costs you everything from the human side of your lineage. Want the extra human skill proficiency? You lose everything elven about your character except the cosmetic details and a modestly better ability to survive being age-drained by a ghost simply by virtue of a longer natural lifespan - which, let's be honest, is practically meaningless in 99% of actual play. How many player characters, regardless of species, end their adventuring careers by dying peacefully of old age in their sleep?
We are losing a middle-ground option that allows people like me, who want mixed-ancestry characters to at least have the option of drawing something mechanical from both sides of their character's ancestry, to lean into how the choice of character species shapes that character. Species choice does not replace things like their background, culture, religion, etc. - those are still very much factors in play, and they contribute to the final whole. But choice of species still matters when constructing a character and the idea that it should somehow matter less, especially and specifically for mixed-ancestry characters of all people, boggles my mind. Why should choosing for your character to be an elf instead of a human be more mechanically significant than choosing to be a Khoravar?
I know it's not intended to be viewed this way, but it feels like erasure, and I'm fairly convinced that the only result is that more mechanically minded players will gradually just stop playing mixed-ancestry characters at all, because it's a choice that effectively no longer means anything, like eye or hair color. The current playtest ruleset reduced mixed-ancestry to a coat of paint layered over the character's mechanical framework and nothing more - useful for roleplay if you choose to lean into it, but practically nothing else.
I know I can just use the '14 Half-Elf statblock, or wait for a third party product to tackle it, or simply homebrew it myself, but that's not the point. I don't like the prospect of a mixed-ancestry people with a shared mechanical identity being split up and filed away as nothing more than mechanically meaningless ethnicity options for their parent species, and I don't think it's a good way for D&D as a game system to go about representing such characters, especially in light of the stated goal of wanting to promote and expand such representation.
