...keep the origins as they are, just remain as recruitable companions rather than characters you can start as...
Oh my goodness, I hope not.
I *really* want to play as the origin characters, starting as them and letting each of them be the *main* character on various play-throughs.
To me, that's WAY more interesting than trying to push a custom character into the main role. I'd rather play a character with an actual backstory that the game acknowledges, instead of a backstory that's kind of just in my head. There's so much more a story can do when the story knows the character and lets you make moral decisions and such. For instance, how would the world react if Astarion was a good guy who wanted to save the tieflings versus Astarion being a bad guy and wanting to join the goblins.
With multiple origin characters to choose from, I get multiple backgrounds to play in a game that actually acknowledges the unique background.
Instead of me playing my blah drow who once upon time did blah thing, or so I vaguely sometimes imagine in my head.