The three valve seems to make a power improvement on the 5.4 and ford is working on the 4.6 3valve for the mustang. I think because of the variable cam timming, the 3v head will replace the 2v head in the next few years to help lower emissions. The basic performace design is there, just gonna need a way to make it work for a performace ugrade on older cars.
I don't believe you will be able to do a swap without some extensive modifications. Remember the Variable Cam Timing is activated by oil pressure, so there has to be some kind of additional passage in the block that flows in to the passage in the head which then in turn controls the VCT.
Maybe some kind of adapter could be fabricated, but until we see the heads & block seperately there is no way to tell.
The new 5.4 3v does have the VCT that is oil feed and controled by the pcm. I pretty sure that the heads that I saw were either prototype or off a falcon and had pressed on cam gears with no vct. The head gasket looked similar if not the same but untill someone puts all the pieces side by side to compare well wont know for sure.