You're right, but the thing is... do we know that? I don't really follow the streams too often, so I apologize if I'm wrong right off the bat, but I feel confident enough to say that - right now - we don't know for sure whether any of that will happen. Is what you're describing really the case here?
Yes, Josh stated that we will get to know his story on his last Q&A - a really weak Q&A tbh. Maybe we will get to know his story through the game, like we did with Durance. But, like someone already said, why would I take a sidekick if I can take a full companion with a relationship system? I would only consider that if the sidekick would be really funny and interesting, maybe getting the sidekicks into the relationship system would fix their problem.
Pretty sure you can still talk to him (and other companions) on the ship, so you probably don't have to take him with you to learn his full story.
Actually, they did an AMA and the sidekicks have an intro conversation when you recruit them but can't converse with them beyond that. So either:
A) Rekke's story will be revealed through outside means like books, or
B) He has more going on than the other sidekicks, and is related to the story for spoilery reasons.
