The Ardling is no more for the 2024 Players Handbook. Altho there is some fondness for it, the survey feedback for the second version of it remained poor. A main criticism is, it is mechanics without a story. To be fair, I have sense of their story − from looking at 2e Beastlands, so the link with Guardinals and Beast Lords (2e Animal Lords) is clear enough. The designers have this in mind too. But 5e has been silent about the Upper Planes. If the UA Ardling description explained its connection to the 5e Tabaxi, that might have been enough story. Oh well. Too bad it wont be in 2024 core to make humanimal concepts accessible, like Aaracokra and Tabaxi and many more. We probably will see the Ardling again somewhere in the future. But since it wont be in the 2024 Players Handbook, I removed the Ardling from the Original Post. I intended to modify some of its mobility traits anyway for better balance.
Now that the Ardling is out. There is no conflict with the Aasimar species being core. It is popular, parallels Tiefling, and deserves to be in the 2024 Players Handbook.
Genasi needs to be in the 2024 Players Handbook, as it is more popular than the Gnome.
Good Celestial angelics: Aasimar
Neutral "Primordial" (!) angelics: Genasi
Evil Fiend angelics: Tiefling
Lets look more in depth at the Aasimar. Since the name is a bit distracting, maybe respell it Awsimar? Maybe call it something else entirely? I am ok with calling the species "Angel". Angel can mean various things, including a human transfiguring into an angel. "Angelic" or maybe Greekesque Aggelikos, Aggeloi?
Think on the name. Aasimar parallel Tiefling. Tiefling have three Fiend Ancestries, and by implication, seven. Similarly, the Aasimar.
The three Celestial Ancestries of the Aasimar would be: LG "Montan" (Mount Celestia, here understood as "the" Mountain of the Celestial planes), TG Elysian, and CG Arboreal.
All seven Celestial Ancestries would be: LLG "Arcadan", LG Montan, GLG Bytopian, TG Elysian, GCG Beastlander, CG Arboreal, and CCG Ysan.
Brief notes about the more obscure planes.
LLG Arcada is a realm of architectural order and it fits to add shopping "arcades", namely passageways of repeating arches with shops along them. There is an obscure LN Astral species, Mercane. They are "quiet money" owners of multiplanar corporations that buy and sell artifacts, relics, and other powerful magic items. I am thinking of making them the "Angel" of the Lawful-by-Lawful-Good plane of Arcada. 5e Spelljammer mentions the Mercanes. Arcadia is a reallife ethnic group, making is problematic to equate with a specific alignment. But Arcada as in "arcade" works suitably.
GLG Bytopia is a plane of Gnomes. It makes no sense that only Gnomes can be the Good-by-Lawful-Good alignment. It is fine if some Gnomes are there, but the plane needs to be about more. I have in mind the dimensional opposites: Up versus down, Right versus left, Forward versus backward, and Past versus Future. This would where the multiverse derives its space-time fabric.
GCG Beastlands is familiar by now. The Aasimar with a few feat choices would actually absorb the Ardling.
CG Arborea. Formerly the Eladrin, who is now full-on Elf. "Arbor" means "tree". So a plane of forests and plants works well. The Angelic would be something like Dryad-Treant species.
CCG Ysgard. The concept of Chaotic-by-Chaotic-Good works well as a realm of personal freedoms, choice, and nonconformity. Actually, Ys in Norse (ys-) means "the commotion of crowds", which evokes crowds of extremely diverse persons in community together. The presence of fiery Múspelheimr and earthy Niðavellir already suggest elemental themes. Maybe make Ysgard a realm where the Elements are highly responsive to the desires of each individual. By extension, the elemental powers that can associate with Aasimar, especially the PF Aasimar, can all come from this plane Ysgard specifically. Norse are a reallife ethnicity, making it problematic to equate them with a specific alignment, especially since the reallife traditions referred are incongruous with the assigned alignment. But it seems for the inhabitants and elements to behave in highly individualistic ways. If so, the name Ys works well enough.
I have in mind an Aasimar with special feats organizing by plane.