A new job listing from Apple has prompted speculation that the iPad isn't going to be the last new platform to run iPhone OS. The advert - for an Engineering Manager in the Core Platform team - asks for "a talented and inspired manager to lead a team focused on bring-up of iPhone OS on new platforms"
"The Core Platform team within Apple’s Core OS organization is looking for a talented and inspired manager to lead a team focused on bring-up of iPhone OS on new platforms. The team is responsible for low level platform architecture, firmware, core drivers and bring-up of new hardware platforms. The team consists of talented engineers with experience in hardware, firmware, IOKit drivers, security and platform architecture." Apple job listing
Among the job responsibilities, Apple list "working closely with the hardware and custom silicon teams to bring-up new platforms and prototype systems" and "defining the software roadmap to support a range of hardware platforms, including iPhone & iPod." That would certainly seem to suggest that Apple are looking to extend iPhone OS across more than the iPhone, iPod touch and iPad devices it's currently found on.
What those devices might be, however, is the subject of some argument. Apple could choose to load iPhone OS onto existing products in their range - though only Apple TV seems a true potential subject, and even then the up-close UI of iPhone OS seems to sit apart from the set-top box's interface requirements - or they could push out new sizes of iPad and other new products.