My best guess is it will be a dual core chip - as you mentioned, possibly some variant of the existing A5 chip.
IMO we will see quad core chips in an iPad before we see them appearing in an iPhone - much like how we saw the iPad get the A5 chip before the iPhone did.
Someone correct me if I'm wrong but aren't current quad core processors incompatible with US LTE networks? I'm referring to the US variant of the galaxy S3/HTC one X being dual core while the European versions are quad core.
Besides aren't quad core chips very power hungry? My friend with a HTC One X (quad-core) is constantly complaining about his poor battery life. I think I would prefer dual core + good battery life over quad core + not so good battery life.