If Karlsson gets fully healthy he is by far the best of the bunch so you have to take a risk on him, I think.
No chance (and Karlsson has been one of my favorite players in the last 10 years). But, nobody in their right mind even considers taking him over Carlson, Josi, Doughty or Pietrangelo right now.
For one, he's already lost a step, even before the current injury. He's never been as solid as the others in his own zone, yet he was able to make up for that (plus some) due to his speed, acceleration, hockey IQ and absolutely elite level offensive production. Today, 3 of those advantages have been curbed. Karlsson has lost some of his speed and acceleration--and he is no longer the king of offense from the blue line.
That said, after Carlson, Josi, Doughty, Pietrangelo--I would choose Karlsson based on skill--then cross my fingers and pray he can stay healthy.