Having 5 custom origins takes the same resources as having 5 "origin" characters. It is not impossible. People are already offering ways it can be implemented like adding tags for those stories. It is a choice of what do you want to develop, choices for custom characters or more "origin characters" that cater to Larian's tastes instead of player's.
Now, Larian said that custom characters won't be penalized as opossed to the origins, so I would hope that they are looking for ways to make playing a custom character as good as it is to play one of the origins. You should be penalized for liking custom characters over the origin characters. And right now it feels as if the story is about the origin characters, not the custom ones.
On the other hand, it is possible that you are only allowed to play custom characters right now because they are gathering info that would be used to create the custom tags. I hope this is what happen.
