There are 3 routes to take:
Madara
Madara becomes the final villain and it's every single person against him and his 'God Tree'. There's another epic finale and it's over.
Sasuke
Sasuke and Naruto may require a small timeskip and will have a power struggle over the future. This could potentially turn out to be fantastic. Whether it's a figght that's personal, blood-lusted, political or just to show their respect- it would be a good ending. And I kinda want it.
Orochimaru
This seeds have been set for a while. With Obito out of the picture and the Hokage and Madara still mysteriously around...it might just be his time to shine. Orochimaru has the current capabilities in his grasp to take control of all 4 Hokage and this may have been the opening he was waiting for. Madara is finally defeated and the fake ending of the show takes place when- Orochimaru smiles and becomes the strongest living thing in the Naruto Universe with the combined powers of DSM and all 4 of the Hokage. This is very difficult to guess whether this'll happen or not but if Kishi wants to take this route it would not only be fantastic, but my personal favourite ending to the manga.