All we know about the Shadow of Mordor sequel are based on rumors, leaks, and speculations but what we do know is the things that fans would like to see when the sequel arrives.
As interesting as the first game was, fans said that things started to get a little boring towards the end because they were stuck in Mordor doing the same thing over and over again. Some of them think that it would be nice if the developers allowed them to travel outside of the Mordor in the sequel.
It would be interesting to explore the rest of Middle Earth and see what is going on outside of Mordor before the Fellowship of the Rings event started. Other are hoping that Monolith would do more to the Nemesis system.
Monolith themselves has never indicated that a sequel is going to happen although the fans seems to believe that it will.