Dana White has confirmed on multiple occasions now that he intends to have BJ Penn and Georges St. Pierre fight each other if St. Pierre beats Jon Fitch at UFC 87. However, it's never been clear if Dana was willing to let BJ Penn hold two titles at once. There are obvious problems with that sitiuation, the primary one being that with one guy holding both, each belt could only be defended once or twice a year.
This is not confirmed, but a fan over at The Underground says that BJ Penn was on a Hawaiian TV station and spoke about the fight:
they will be fighting this december 27.(source is bj penn his self on hawaii local news) the fight will not be a title fight but its going to be announced as "battle of the weight divisions". if all goes to plan hopefully gsp will still be holding the ww title after they fight in december and bj will move up and fight gsp in hawaii for the ww belt.
The only reason I'm willing to buy this is that it gives them an opportunity to do a meaningful rubber match if Penn wins. The downside is that the "battle of the weight divisions" will probably only be a 3 round fight.
Of course, it may turn out this guy is just making stuff up. As they say, developing...