The Thing Everyone Missed About The Seasonal Content Announcement
ZOS workers recently unionized right before they announced the new content model. I think these two things are related. The team likely wanted a different workflow and now that 450+ of them are in a union, they have more leverage to change the working conditions. It might not have anything to do with sunsetting or maintenance at all but rather the dynamics of a unionized workforce versus a non-union workforce. The workers might want to do smaller chunks of content rather than big expansions. Seems like a big thing to consider before running straight to "MaINENanCE MoDe" declarations.
Also a unionized workforce likely means the game will continue longer as the union will want to ensure that they keep a healthy number of quality jobs.