I think Crosby and Malkin can play on the same PP unit (although I would prefer a 1A 1B PP unit with them separate) the key is to get Crosby down low on the goal line. I remember the year we won the cup in the Caps series when OV and Sid had hat tricks, Sids last two goals were from right on the goal line digging for rebounds. I feel with Sid down low his passing can be used for great one time feeds and it also allows him to quickly get to the net and use his great hand eye coordination to put in loose rebounds. Think about the threat of Geno's one timer from the right circle rebounding of the goalie right to Sid to put it in, and if that doesn't work just play the puck a little lower and Sid finds a cutting Neal/Letang for a great back door play.
So I think it can work, but since both Geno and Sid want to play the half boards then give them there own PP units and see how that goes. For how much DB juggles lines at times and stuff you would think he would at least try and change up the stagnant PP units. Also I hate when Geno stays out for 1:30-2:00 of the power play .