GAH!
Took me forever to find this thread, I think it needs a different subject line because it's a good topic.
I also am curious what they plan for the next major holidays. As long as they continue updating, I plan on keeping going. I probably won't be as obsessive due to real life but I will definitely continue to be a daily player (barrng issues with the game or no more updates).
My son made me buy him all the Treehouse of Horrors on iTunes so I think there is still a ton of content available for Halloween. The one where they mocked Nightmare on Elm Street and made Willie into Freddie and the Lard Lad and all the advertisement coming to life and terrorizing the town come to mind. There is plenty of content.
I think Christmas may be a bit harder to make fresh and new.
I don't think they will remove what we already have but I have no idea how they would do Christmas different.