Kobold Avenger
Legend
I think they're only starting to consider other Celestials because Planescape is on the way.1D&D has three celestial legacies- Exalted, Heavenly and Idyllic for their new Ardling race. I would use these three legacies for the Aasimar instead. The Idyllic legacy should be for the those Aasimar who are the descendants of the Guardinals (In PF1, there's the Idyllkin Aasimar). The Heavenly legacy should be for those who are the descendants of the Archons (who are from the Seven Heavens ). And lastly, the Exalted legacy should be for those who are the descendants of the Angels.
The problem with the Aasimar in 5e is that they are too angel-centric. Which is strange because angels aren't the only kind of Celestial in 5e.
I think somewhere in 2e, the metallic/alchemy-themed Rilmani of the Outlands have also been considered as possible ancestors of some Aasimar. If they return in 5e they'd probably be of the Celestial creature type.