To recap. In BG1 and BG2 you have a story and quest of your own. You were a Baalspawn.
In DOS1 and DOS2, the origings stories have a story and quest of their own + main plot. Custom characters only have the main plot.
In BG3 we follow the same pattern as DOS1 and DOS2. Origin characters have one more tag that provides a story and a quest. So, why won't they create tags and stories that can only be selected by custom chacters that provide an story arc + quest on their own. That is basically what Dragon Age 1 did. You don't need that many stories to choose from. At least if you do relatively generic ones. I mean, a red wizard story would be really specific and only available to human wizards. But someone who lost their family to goblins, might work. Or if you want to be have more conflict, to undead or githyanki (that would cause lots of drama XD). Then you have other classicals, like stole/find something quite valuable that many people are seeking. Like a netherese artifact that you can't get rid of. The trick is to use elements that are already there so it is easier to integrate in the main plot.
So, basically, what do we have on the first chapter?
Githyanki, vampires, goblings, drow, illithids, zentarim, harpers, svirneflins, the light society and netheresse. Well, they could work out stories linked to that. If I had to write some stories, I would probably choose:
Harper
Zentarim
Light society (the one with the bugbear and the illitid), this could be linked to the netherese investigation.
Undead hunter (Even if I like Astarion)
Blood money (stole a powerful netherese object that you don't know how to use. Although I suspect that this is shadowheart thing XD).
My point is, they have already done that for the original characters, but haven't even created one for the customs. Being able to play the quest for the origins characters doesn't make up for not having at least one that is exclusive to the custom character. And no, "baldurian" doesn't cut it, because it is not a personal quest. Neither is the tadpole.
They said that custom characters won't feel lacking. So it would be nice to provide a personal quest and a little more dialoge for the custom character.
