What you're both describing is the theoretical player you'd want to replace Skjei. A top 4 stay at home, shut down D. Is it possible Hajek or Rykov could one day become that player? Possibly. But that doesn't describe the roles either of them have played through their careers. Or are capable of in the NHL right now. They were both more of a hybrid defender similar to Skjei -- but not as good, at least not yet.
The young player you're describing is Lindgren. And he's a bit overmatched playing as a regular #4. There is NO current internal replacement in the NHL or AHL that is ready to step in for Brady Skjei as the #1 LD. That player would need to come from outside the organization. I'm happy to challenge young players and give them a little more than they think they can handle. And that to me is what we're already doing with Ryan Lindgren. Lindgren is currently more stable than Hajek or Rykov in his own zone. I would not move Lindgren any higher than he is already. And I would not thrust Hajek or Rykov up there either. That's putting too much pressure on them. At best, it's a Neal Pionk situation all over again. So, that means your only replacement for Skjei is... Marc Staal.
I understand the desire to upgrade both the forwards and the left side of the D. I agree. I don't agree that trading Skjei is likely the best solution for the development of the other young players on the roster. Not unless you're trading him along with another piece to upgrade the position he currently fills.