I'm going to take a wild guess and say that it won't have the ability to swap battery's...the battery size is probably a way for nokia to have made the device cheaper (as is the screen size) and adding the ability to swap batteries would add to the cost.

If you're going to introduce a new device class with a new operating system that no one has ever heard of, you're going to have to avoid cost from further inhibiting potential users. Or, you could choose to blow away the competition with the specs to justify the price and the risk of the new platform, but by the time this gets released it won't be anything extraordinary with regard to the specs so this obviously isn't their plan.