If they were to do a hypothetical 6e, I imagine Aasimar or Tiefling might be closer to how they did Lineages in the recent Van Richten's book.
This is more or less how I'd do "race" if I were in charge of 6e. Use either "kin" or "folk," group various things together into one common umbrella. Humans ("Wanderfolk," because--rightly or wrongly--other folk see them as being unable to settle anywhere, they keep going and moving and searching) would include a Dual-Blooded lineage, which would give a package of subrace options instead of the usual "humans can do anything" generic package of a feat, a trained skill, flexible stats etc. It'd cover tieflings and aasimar, but also half-orcs, half-elves, muls, genasi, etc.
The upside to this is, you start having (more or less) the same flexibility that class/subclass provides. That is, instead of needing to publish more "complete"kin, you can do so sparingly, only when it's really needed, and instead just publish more subkin for existing options. E.g., one of my proposed kin types was Beastkin, which covers a variety of anatomically-distinct (but related, because Fantasy Genetics) options like tabaxi and minotaur. Instead of publishing an entirely new kin for loxodon, you could just make loxodon one of the options within the Beastkin umbrella.
"Kin" or "folk" also has the advantage that they
are already used in some places/games (e.g. Lizardfolk, Beastkin, the fae folk, Pathfinder's various "<thing>kin" aasimar variants), so this isn't an unprecedented leap--and "kin" is allowed to mean a broader range of things than pure blood relation, e.g. "of the same kind or nature; having affinity." So you can have Ashkin (the FFXIV term for all undead) despite them being united by the way they
became what they are, rather than united by any blood link.