if i might tangent this thread a tiny bit to a similar topic, if doing the same thing with species what would you pick as the '6 species'? i think i'd have:
Humans-versatile, offers lots of customisable skills and proficiencies, advantages to charisma/social interactions building off their description in the PHB as 'everybody's second best friend.'
Smallfolk-halflings and dwarves, gnomes and goblins ect..., as the single 'small' species allows the to go into more depth of the mechanics of being a small species giving them unique pros and cons than the other species.
Giantfolk-goliaths and giants, ect..., as the single 'large' species allows them to go into more depth of the mechanics of being a large species giving them unique pros and cons than the other species.
Planetouched-elves and tieflings, assimaar and elementals ect..., the 'magic' race, limited degrees of inherent spellcasting or more 'supernatural' capabilities.
Beastfolk-dragonborn and orcs, minotaur, lizardfolk and tabaxi[?] ect..., customisable with a point-buy style list of various generic beastial traits like fins and gills for swimming and waterbreathing, wings for gliding, claws for digging, extra or enhanced senses, natural weapons like teeth, horns, claws, breath weapon or natural poisons/paralytics/ect...,
Constructs-Warforged and other similar material golem types[?], plantfolk ect..., they're tough and sturdy, resistances to damage or certain types of status conditions, bonuses to health, they don't have standard biological needs like sleep.
Interesting choices. I personally prefer to go for less "grab bag" and more "do one thing and do it well" options, so probably...
Humans: Bog standard, they have to be there. (Though I'd prefer it if games were less
painfully fawning about how special we are...)
Elves: Gotta bend to the will of the crowd on this one. They're just too popular, and have been for ages.
Dragonborn: Because I think they're awesome. 'Nuff said.
Orcs: Sort of a counterbalance to Elves, while being more down-to-earth than Dragonborn.
Dwarves: But with a twist--gnomes and halflings are
also dwarves, just different cultures.
Hybrids: The only grab-bag, and for a reason, they blend two other options together (and allow for being partly some non-option, e.g. tieflings, aasimar, genasi, etc.) Any two of the above can be half of your parentage, so you can be a tiefling with a dragonborn parent, a dworc, etc.
This presents an interesting possibility of having different races as opposed poles to one another. E.g. perhaps dragonborn and orc have some kind of special opposition to each other for some reason (maybe orcs have giantish ancestry here?) Elves and dwarves are a classic opposition. And then we could have humans opposite the (non-playable) "weird" planar creatures, simultaneously driven from and driven toward these alien beings (hence all the Hybrids), and Hybrids sit in the middle. Maybe dragons are Astral-coded and orcs are Elemental-coded (like giants?), and perhaps we can associate the Shadowfell not just with death and darkness, but also
industry and
ennui, while the Feywild becomes a place of energy unto mania and excess unto extravagance, when either one is allowed to ride roughshod anyway.
That gives a pretty solid cosmological form. Dragons from the plane of laws and thoughts (but drawn to material wealth and energies), vs giants from the plane of forces (but drawn toward concepts and hierarchy). The grinding, entropic clockwork of existence and death (but encouraging industry and motivation), vs the lackadaisical, slothful excess of extravagance and hedonism (but encouraging creativity and excellence). The grounded, here-and-now attitude of the mortal world (but the yearning for adventure and fantasy), vs the otherworldly, alien goals and interests of the distant planes (but the yearning for participation in something concrete).
Less "law vs chaos" or "good vs evil" and more Daoist "forces that create their own opposition," forces that can never truly be separated and which instead achieve something greater when one strikes the correct balance between them for each individual situation.