Zenimax only has a handful of trademarks related to TES, and each and every one of them have been used as the name of a game or DLC. All except one, which is Skyrim. They've had this trademark since 2006, and it's about to expire. Well, actually they have 3 Skyrim marks about to expire. Zenimax extended their expiration dates until they used the maximum number of extensions, the latest extension being earlier this year, and these extensions made people think they're using it for something as they wont let it expire. But people still had doubts. That is until they filed for a brand new Skyrim trademark a few weeks ago. Not the name of another province, they trademarked Skyrim, yet again, and this trademark wont expire for another 3 years. This essentially means it is
extremely likely they're going to call TES V Skyrim, unless they like spending money on trademarks for the hell of it.