Remathilis
Legend
So you're going to run into a trifecta of immovable problems here: backwards compatibility, verisimilitude, and customization/complexity.I still don't understand why "Well, we can't condone min-maxing" is a suitable justification for not even trying to develop a system for mixed character ancestries.
The only way you get hybrid/Build-a-bear system to work is if every race is built using a system where they are designed fairly equally. That is, you create a point system and every race in the game is balanced to it. Obviously, with nearly 100 different species in the game, that would be redoing them all from scratch. They are deathly afraid of invalidating older material, so that's a no-go.
If given a choice between standard packages and build-your-own, most experienced players will build your own. The ability to swap out weak, uninteresting, or redundant features for better or more useful ones. Players will use for no other reason than people love eeking out extra advantages.
Which will eventually lead to a game where everyone is a hybrid. NPCs might be elves, dwarves, and humans, but every player will want to be a hybrid. If any combo is particularly potent, that one will show up with consistency. We used to joke how in 2e, unless you were aiming for a paladin, half-elf was strictly better than human so our games were full of half-elves and rarely humans. I imagine the same would be true here. Unless the hybrid system produces characters weaker than their parent races, you're going to see hybrids and only hybrids (barring noobs and role-players).
That is a bad mix of problems. And I don't want players opting for dragonborn/tieflings strictly because it's a better combo than dragonborn or tiefling alone.