In the past it were Batavia and Gralus who organised the exposition. And I'm sure the new host will not have it easy to do it better then Gralus.
Nations that joined the exposition the last time were:
1. Gralus
2. Stormark
3. Natopia
4. Batavië
5. Universalis
6. Vlaanderen
7. Republiek der Nederlanden
8. Interland
9. Livlandia
10. Nelaga
11. Shireroth
12. Verac
13. Victoria
14. Imperium Incognita
They have, of course, more chance to host the event.