Ubisoft is currently possibly hinting at a new Ghost Recon game, which some may have found in the form of an Easter egg in the current [game title]. Operation Oracle Update assume.
It contains an invitation to an event hosted by the fictional company Skell Technology, which states:
“This invitation to “Shell Con” takes place on May 9, 2019 at 11.30am PDT, 2.30pm EDT, 7.30am BST, 8.30am CEST"That's next week, right?"
Therefore, some kind of announcement is expected on May 09th, which, according to further speculation, doesn't necessarily have to concern Ghost Recon. A new Splinter Cell game could also be somehow connected, given that the franchises share fictional names.
We'll probably find out more by May 09th at the latest. We'll keep you updated.
(Update)
Ubisoft has now announced a world premiere event for that date, called the Calling All Ghosts stream. Whether it will be a new expansion or a completely new game remains to be seen.