To compare to it's most recent rival, Pathfinder: Kingmaker, Kingmaker started out with playable Clerics, Wizard, Fighters, Rogues, Bards, Barbarians, Monks, Paladins, Rangers, Druids, Sorcerers, Magus, Inquistitors, and Alchemists, each with at least 3 Archetypes, plus bloodlines, domains, and so on. It later added Kinetist and Slayer classes, each with three archetypes. The 5e PHB has the Clerics, Wizard, Fighters, Rogues, Bards, Barbarians, Monks, Paladins, Rangers, Druids, Sorcerers, Warlock. That is 14 classes with 42 archetypes plus numerus bloodlines, Domains, ect.... vs 12 classes with 39 subclasses. Add in Slayer and Kinetist and that is 16 classes with 48 subclasses.
It also had 8 races to start with, Human, Elf, Dwarf, Hafling, Half Elf, Half Orc, Gnome, Aasimar (with Regular, Garuda, Angel, Archon, Guardinal substitute, Azata, Peri subraces.) Then added later Tieflings (with Regular, Oni, Demon, Devil, Kyton, Daemon, Div, Qlippoth, Rakshasa, Asura subraces.)
So BG 3 tries to be competive with that, it will have to have all the PHB classes and subclasses, races and subraces at minium, but that still won't be as many options as PF: KM when it comes classes/subclasses. That is
Human, Human Variant,
Elf (Drow, High Elf, Wild Elf subraces), Dwarf (Mountain, Hill), Halfling (Lightfoot, Stoutheart), Gnome (Rock, Forest), Half Elf, Half ODragonborn, Tieflings. That is 8 races with 7 subraces vs 9 races and 9 subraces. If you add in PF Tieflings that is 9 races with 17 subraces.
To stay competitive, I think 5e will have to have more then just the PHB races, subraces, and subclasses, as 5e doesn't have anywhere near the classes the PF: Kingmaker does which is just a fraction of Pathfinder classes period. One area that 5e could gain an advantage is races and subraces.