Ah, my mistake.
Swapping Niskanen for Regehr is at best a lateral move with the way Niskanen has been playing. He's playing upwards of 21 minutes again (now that healthy), on one of the top defensive units in the league. Regehr is playing 17 minutes on a very bad defensive squad. Sure his style of play is something that's needed, but can he play 20+ minutes a game? I wouldn't mind adding Regehr as a #5, but that means no Niskanen in the deal.
And even adding Pominville's salary is a little much for next season. We could make it work, but given the cap decrease, I think there will be lots of options out there, so I'd only do this trade if we could get a steal of a deal.