Word is coming down thanks to NeoGAF that Ubisoft is currently working on a new Splinter Cell game, and Michael Ironside is reprising his role as Sam Fisher.
The poster, Crossing Eden, is notoriously reliable for their accurate leaks coming from inside Ubisoft. One of Eden’s sources dropped details on Watch Dogs 2 as well as Assassin’s Creed Syndicate, and each time the sources were completely correct. This source provided the following nugget of information:

Regarding other games, I haven’t been involved with Steep or Wildlands, but I was surprised Splinter Cell didn’t appear at E3. I know Ironside is back. He was in the studio, I said Hi to him and his daughter. He was shooting a movie with Amy Jo Johnson, and I know someone who worked on that set and Ironside confirmed to him he was doing the new Splinter Cell. I know Toronto has the mocap studio for it. I’m hoping to hear or see something unofficial, if not official, this year, but its been hard to get anything beyond ‘It’s Happening.’
Eden later update their post, saying that they heard back from this source who saw Ironside in Toronto while he was in town shooting a film, The Space Between. While he was in town, he reportedly dropped by the Ubisoft Toronto to work on the new Splinter Cell.

To throw a date on this: I did see Ironside and one his daughters at the TO studio last summer. This was just good timing, as I was there on other business.
I have two sources...