With the surprise blockbuster success of Elden Ring, Splinter Cell could do well to do the Ubisoft thing--meaning copy its formula outright to spice up their played-out open world style.
I'd want to play as Sam Fisher, dropped into the capital city of a third-world country and its outskirts. A colossal screw-up from leadership leaves you cut off from your team, their intel, and all your equipment. You start from scratch. It's an open-world experience where you know from the start that you have to take out the dictator in his big fortress/skyscraper/mansion/whatever in the middle of the city, but how you get there is up to you. Non-linear storyline with a dozen ways to reach that goal, New Vegas-style.
Exploration is rewarded through unique story beats and equipment to help you get closer to your goal. NO SKILLS LOCKED BEHIND PERK TREES. All moves open from the start, but your equipment is what opens up new opportunities of approach. The only map icons you'll have are the ones that you marked yourself. Stealth is required throughout, since you're fragile. The power fantasy and sense of progression comes from connecting with different supporting factions and gaining access to better equipment rather than Sam Fisher suddenly remembering how to do a jumping wall split after having been an operator for 20 years.
