If the Kings want to spend $9M on a center, I suggest they give that money to Johansen when he becomes an UFA.
He may become a free agent, but it's rare that players like him do. He's a legitimate alternative, but an unlikely one.
You never see players like him in free agency, trading for a guy like that is almost not worth it for what you would have to give up(unless you luck out and get Joe Thornton for nothing), and all that leaves is the draft, which can be a crap shoot even with high picks.
For better or worse, my guess is the Kings will be stuck with a big contract Kopitar. You could trade him before he hits free agency, but the return won't be as good as it would with a signed Kopitar. If he's signed, you wouldn't trade him. If you did trade him, who's he getting replaced with? It's not like Carter is getting younger either.
Yeah, it's a situation that any successful team will eventually find itself in. The job for Kings management is to keep the cheap prospects coming. They do that, they can extend the success. If they don't, they'll end up where the Devils are right now.