Orochimaru is one of the three legendary Sannin of Konohagakure. He is one of the most creative scientists around. He has prolonged his life and stayed young by changing bodies. Oro already knew how to use the Sage Mode of Cave Ryuchi but didn’t find a suitable body with he could practically use it. But it is possible that he has already found the body with which he can use the Sage Mode, and hence we might get to see this new Sage Mode user.
2. Sarada Uchiha
Sarada Uchiha is the daughter of Sasuke Uchiha and Sakura Haruno. She wants to be the Hokage and is an admirer of of Naruto Uzumaki. If Naruto Uzumaki will be the one to train Sarada Uchiha, then he won’t only teach her Rasengan and toad summoning techniques, but also the Sage Mode of Mount Myōboku. Thus, we could see Sarada as the new Sage Mode user.