The Nationalities/Fleets in the Core Book are:
- British
- French
- German
- Austro-Hungarian
- Italian
- American
- Japanese
- Ottoman
- Edit: I missed Russia somehow! Russia is also in the book!
There maybe some additional content on the Osprey Website that will add a list for "Regional Powers" that pull largely from the Nations listed above for general ship profiles. There may also be 1 or 2 additional ships for each nationality as well.
There are currently no plans for expansions at this point, but I have all ready received requests for expansion into several areas/regions, rules to make your own airships, and other ideas. If it sells well enough, perhaps. However, Osprey is typically risk averse to "secondary books" unless the initial ones sells incredibly well. Expansions typically do not do that well.
However, I plan on supporting it with future development via my Blood and Spectacles Blog and Wargame Vault.