Sam Fisher is on his way back, but not in a whole new game (as far as we know), but in a remake of the first game.
The remake will be made in Snowdrop Engine, which has been used primarily in The Division games. Matt West from Ubisoft says that they are still early in development and that the game is being rebuilt from scratch. However, they want to maintain the spirit of the original game, and for example, it will still be about linear paths rather than an open game world.
Ubisoft Toronto is responsible for the development, and they themselves state that there are many veterans in the team who have worked on previous Splinter Cell games. They say they want to build a stable base for Splinter Cell's future, and in the video above they also say that "the return of the series is glimpsed on the horizon". It therefore sounds like the series may be revived seriously, unless they just refer to the VR game that is underway.
We do not yet have a release date for Splinter Cell Remake, nor do we know which platforms it will be released on.