IMHO the only guarantee on the next version is increased storage capacity.
...at this point everything is just speculation...
Very true, but it's reasonable to expect more than a simple memory upgrade - that'd still just be a 3G. There is nothing wrong with speculation, as long as it is educated. After all, the world works around trying to predict and plan for the future, be it starting a business, marriage, saving for education, insurance, retirement, etc. For example, one may invest in a business because they speculate that it will succeed, but a wise investor will have a good degree of confidence in the company which may come from research about the company, foresight about the usefulness of the product, etc.
The very minimum to expect is an improved camera. The camera quality was criticized on the original on the basis that it was substandard to other smartphone cameras on the market. That is even more true when the 3G was released with the same camera. There is no chance that Apple will release the next model with the same camera if they want the phone to be a success, not to mention by that time it will be the same technology of their two year old phone.
Hardware improvements in processors and RAM are just taken for granted these days, but it will be even more important in the iPhone with all the apps available and those that will be coming. If the iPhone was considered more as a mobile
computer than a mobile
phone, it will only become more apparent as apps are released. Many apps even now have a problem with running out of memory when they run, lagging all the functions of the phone. Hopefully more efficient software development will improve things, but the amount of RAM is still a hardware limiting factor, and to really keep up with 3rd party app development, the iPhone is going to need more.
And finally, what else is there to improve that you can't get through software revamps? It's not like the 4G network is going to be ready, and it already has GPS. More internal memory is just a given.
It may be speculation, but really it is the next logical step for the iPhone that I don't mind betting $580 on.