OK, we may agree some "racial traits" aren't really inborn but based in traditional upbringing, and this detail can cause troubles if "transhumanist magic" is possible, I mean, trans humanism like Eclipse Phase RPG or Altered Carbone, when memories can be uploaded to "file" and this downloaded to a different body, maybe from a different race. It is not only possible thanks druid's reincarnation spell, but also Savage Species had got a special magic ritual using as example an ogre becoming an elf.
I actually have a character for an upcoming game that switched species (pre-start) due to reincarnation, and so became a transmuter wizard so he could figure out how to turn back.
My suggestion is allowing those "nurture" or traditional upbringing to be replaced with other options. Maybe with some special traits as the dragonmarks from Eberron, or "exclusive feats" only for members of a noble house, religious brotherhood, criminal guild or other faction.
Agreed. Those would be great cultures to go along with lineage. I did two forest-dwelling cultures earlier in the thread. However, care would have to be taken not to overlap these cultures with backgrounds too much.
* Who would want to play a halfling warrior? An otaku who loves the trope of kid hero, for example the main character of the videogame Dragon Quest V. Somebody love the trope of litle people defeating kaijus, giants, megafaun and other bigger enemies, but the little PC races weren't designed to be fighters but rogues or maybe spellcasters.
There are lots of reasons: fighting back against enemies who want to take over or have already taken over the character's homeland, a hunter who is responsible for feeding their family, a town guard turned adventurer, and so on. Plus, Small races include gnomes, goblins, and kobolds, not to mention a plethora of 3pp races.
* Besides dwarves and elves, what PC races have got racial traits based in "traditional upbringing"?
Depends. In the Ancestries and Lineages books by Arcanist Press, most racial spellcasting became a cultural thing, with the idea that (for instance) an air genasi raised by other races can't use their innate 1/rest
levitation. That's definitely a possibility.
The main problem is that, except for the main PH races, none of the other races really have sub-races that are
cultural. So going by the various races (and ignoring languages), other than halfling, elf, dwarf, and gnome, I'd say the following could be considered cultural traits (not not every race is here; some don't seem to have
any cultural traits):
Bugbear: Sneay, Surprise Attack.
Centaur: Survivor.
Dragonborn (Draconblood): Forceful Presence.
Firbolg: Firbolg Magic, Speech of Beast and Leaf.
Githyanki: Decadent Mastery, Martial Prodigy.
Githzerai: Mental Discipline.
Goliath: Mountain Born.
Half-Orc: Menacing.
Hobgoblin: Martial Training, Saving Face.
Kenku: Expert Forgery, Kenku Training.
Kobold: Cower, Beg, and Grovel, Pack Tactics.
Lizardfolk: Cunning Artisan, Hunter's Lore.
Minotaur: Imposing Presence.
Orc: Aggressive, Primal Intuition.
Satyr: Reveler.
Tabaxi: Cat's Talents.
Triton: Emissary of the Seas.
Veldaken: Veldaken Dispassion, Tireless Precision.
Verdan: Persuasive.
Obviously, this is YMMV a lot. I didn't include innate spells because it's very unclear whether these are actually truly innate or if they are taught.