Yes, AK can play the PF depending on the matchups, and honestly that is all we need him for at that position. I'd look for him to guard guys like Dirk, Frye, Josh Smith, Bargnani and other 'stretch 4' types.
He also comes in handy when teams go small ..If a team like Miami played Bosh at C and James at PF.
I think his primary role would be as the backup SF .. possible starter depending on how Salmons plays. Salmons is a solid defender, but he is limited by his size. SF's today are just huge dudes. Anthony, Pierce, Beasley, Wallace .. Salmons will struggle defending those bigger forwards. Last season we put Greene on them, and he did a solid job all things considered, but AK is in another league. Much more effective and reliable offensive player aswell.
If we add AK though ... lots of obvious logjams are going to be created. Something will have to give at some point.