The fact is that the developers of Shadow of Mordor never did announce that they were working on a sequel to the game. There were a few hints here and there and then there was that Linkedin leak but that was all we got.
One of the reasons why the fans think that a sequel might be in the works was because the developers mentioned that they had more planned for the whole Nemesis system in the game. Many fans took this as a hint that they might be planning a sequel and that we will be seeing a more advanced Nemesis system in the new game.
The there was the leaked resume where the game Shadow of Mordor 2 was listed as one of the past jobs of a stunt actress. It could have been a hoax or it could be the real deal. Fans were expecting to see the game at E3 this year but that did not happen and things have been pretty quiet since then.
With so little information to go by, all we can do now is wait and see.