Why Pete doesn't play youngsters (and why not on the first line)? It looks like an old story in this part of town so let's break it down. Of course we assume that goal of DeBoer is producing results, not developing prospects who may make impact 5 years after he's fired.
Josefson's production in his NHL career is 25 points in 118 games. He has scored total of 7 goals in those games. Tell me - what could this guy bring to top-six? The answer is nothing. You could use him in bottom-six but once again - you've got much better players on 3rd line and 4th line is shutdown line, Stephen Gionta works much better there. You may not like Gionta but if you try to watch games with open mind, you would notice that Gionta is useful at 4th line.
I think that those who still consider Josefson good player will get their reality check when he's waived and noone takes him as it happened with Tedenby. Tedenby was worse case but it's similiar - not enough grit to play on checking lines, not enough skill to play on scoring lines.
All in all, Josefson didn't deserve to be NHL regular this season and even if he did, his presence wouldn't change anything.