As I personally think that Anno 1800, up to now, is a missed opportunity to better immerse the player into the 19th century politics, it will be a great idea to have an DLC focused on the politics and struggles of this period.
For example:

- a late game quest where you can declare independence from the Queen (has been done in 1701, and I'm really disappointed that it wasn't implemented in 1800, as it was a really good idea, for the Anno series)
- as choosing the independence road, maybe there should be a penalty for that (like reduced output for production, negative balance for a specific time, investors population drop etc.)
- an option to prioritize after either the worker/engineer class to become, or the investor one (either a more social focused society or a money grabbing one), by introducing new mechanics/items than will buff certain buildings etc.
- a quest in which to proper reflect the revolution, those New World guys keep talking about (maybe after choosing independence, the player loses entirely the New World assets, and can choose between war or trade (peace) to get back the benefits of those lands
- also it will be cool, to be able to give certain islands to an NPC, via some kind of contract (giving a Lands Of Lions island to an NPC (Ketema maybe), thus the island becomes independent of the player control, but it will still produce a products, based on a contract)
- etc.

If there will be a season 4 (based on the Tourist DLC I kind feel that will not be the case), but IF, please be it more focused on the politics of the period and bug/optimization fixes.