I would prefer it if 1 D&D kept the Aasimar and the Ardling as separate species.
What part of the Aasimar species to like and care about the most?
The Aasimar, the Tiefling and the Genasi are all planetouched species, beings who are the result of planar beings having one night stands with some lucky (or unlucky) mortal from the Material Plane.

Or in some cases, they are result of being exposed to planar energies while still in the womb. "Mom and Dad had a little 'fun' while trekking across the hellish countryside of Avernus."
Yeah, the term "ancestry" can mean different things. It can mean a sexual reproductive parent. But in planar contexts, it more often means a magical transformation of a Material Humanoid. I notice, in the recent descriptions of Aasimar and Ardling, the "descendants" are typically extraplanar creature beings who materialized into the Material Plane as immigrants, magically becoming Material creatures. These Astral creatures that are made out of thought are becoming clothed in the flesh and blood of the Material Plane. It is an incarnation. Perhaps this entanglement with materiality hides the part of them that is aware of the Astral Plane.
A similar thing happens with Elves. In their case, they originate as Astral thought. But they physicalize as forces becoming spirits of the Feywild. But some of these spirits incarnated into the Material Plane − materializing as creatures of flesh and blood.
As for the Ardling, I like the second idea that WoTC came up when the Celestial angle for this species failed to fly. They originated on the Beastlands, but migrated a long time ago to the Material Plane.
Most Ardlings appear to remain in the Astral Plane, in the dominion of Beastlands. The ancestors had already evolved there into the bipedal humanimals. Some of these immigrated into the Material Plane, becoming the ancestors of incarnated Ardlings.
And they stayed on the Material Plane long enough to see it as their home plane.
It is interesting. Something like a choice. They can use magic to manifest into the Material as conjurations that are made out magical force. These physical forms are temporary. But some choose to take on Material flesh and blood becoming natural creatures within the Material World.
All of the anthropomorphic animal species currently in 5e could be different kinds of Ardlings so as to avoid any confusion between, for example, a leopard Tabaxi and a leopard Ardling.
Since both Ardling and Tabaxi come from Beastlands, it is clear that the Tabaxi is one of the kinds Ardling.
If the Ardling were planetouched, I would like it if they were like the Beastfallen from the
Grimoire of Zero anime.

They would be the result of a magic spell that imbued the ancestors of the Ardling with the energies of the Beastlands.
That could happen too. A natural Material animal is, for whatever reason, transformed by the Divine magic of Beastlands, thus becoming a Material Ardling.
It would be a guided evolution into a bipedal form, reminding me of the recent Guardians of the Galaxy movie.
But I can't see them being planetouched in quite the same way as the Aasimar, Tiefling and Genasi are.
Genasis are obviously Elemental, but I am ok with them being "Primordial" in a sense that is of Astral origin.
Aasimar and Tiefling are counterparts who parallel, because they each can come from several alignment dominions.
The playtest Tiefling mentions three Evil dominions: Hells, Hades Gray Waste, and Abyss. But the Fiends of other Evil dominions can reproduce Tieflings too: Acheron, Gehenna, Carceri, and Pandemonium. The appearances and traits differ by plane.
Same situation for the Aasimar. There are many Good dominions whose inhabitants can reproduce Aasimar: Arcadia, Celestia, Bitopia, Elysium, Beastlands, Arborea, and what is currently Ysgard.
The Ardling that the playtest describes is what an Aasimar looks like who comes from Beastlands.