There's been 4 Splinter Cell games over the last 5 years, but none of them have made it past pre-production and there isn't one currently in production. Every single Ubisoft team is tied up on other projects at the moment, you won't see another Splinter Cell game for another decade, if ever.
What happened to the most recent one? Aka, the one mentioned in the Walmart leak?
It wasn't a full Splinter Cell game, it was going to be a teaser for a downloadable VR Spies vs Mercenaries spin off, PS4 exclusive, being developed by Ubisoft Montreal and Red Storm Entertainment who are currently making a number of VR titles for Ubisoft. It was shit canned.
In 2012 Ubisoft Toronto started pre-production on a new Splinter Cell game whilst Blacklist was being wrapped up using AnvilNext.
In 2014 the Blood Dragon team of Ubisoft Montreal was working on first person Splinter Cell.
End of 2016/early 2017 Ubisoft Paris got handed the remains of the 2012 Toronot project and started prototyping an open world Splinter Cell that would then be handed off to Ubisoft Shanghai and developed in tandem with Breakpoint.