From what I've been able to comprehend from the questions I've asked so far, it would seem Paradox are looking towards an expansion as some sort of catalyst for them to continue patching Victoria 2, whilst adding game-enhancing features as well.
What annoys me is the fact that they seem to be dressing up the fact that it will be a patching expansion, with the idea that whatever else will come with the expansion will indeed by the crux of the expansion, even though Paradox have made all EU3-engined games extremely user-friendly for modding...
Again, it would seem Paradox are happy to release games, and then to change how the games play whenever they feel like an expansion is worthy, so that they can receive more revenue from us the customers, who are willing to pay so that they continue to support improving the game and fixing any bugs that exist.