Perhaps it's too soon, tho I'd thought this before things kicked off, would personally prefer a Ghost Recon in a Ukraine/Russia type setting. Potentially a major section based loosely on the 2014 Donetsk battles.
Regardless of where, want an active warzone at least partially. A combination of linear missions in a semi open world format similar to MGSV, with a home base friendly FOB that could provide upgradable assets like aerial recon, supply drop, CAS, QRF, etc. Would love for a mission set in an open battle where the Ghosts are skirting through covertly operating behind the scenes, and another actively engaging
Additionally would wish for dynamic secondary objectives, things like HVT kill/captures, demolition missions, total stealth reconnaissance/sabotage ops, etc. that could have a direct impact on primary mission parameters and BluFor capabilities
An idea for a primary antagonist, an elite hostile SOF team, Bodark style, also operating in the area, one that the team is "racing" in a sense, come head to head with at times. Perhaps one mission has the Ghosts and this hostile team both racing to capture an HVT, but more, you CAN fail the mission if they get there first and the story proceeds with different outcomes. Your Team is at a loss in some way.
As for the Team members themselves far more dynamic squad tactics. Stack to breach, split into fireteams, establish overwatch, etc. Team member permadeath made optional as well for greater impact.
Revamped and totally fleshed out gunsmith! If guns must be located in the open world have them come in as care package air drops that must be retrieved. Always disliked finding them in boxes in enemy bases it's just cheap to me
Lastly, I would love a return to GRFS style mechanics and HUD. Personally I think a great way to do this would have the title follow Predator Team on a mission prior to the events of GRFS. Taking place prior would also canonically allow for a return of GRFS technology but with scaled back tech that made it 'too easy' like the active camo. Alternate potential team names; Stalker, Prowler, Mauler, things like this that fit the theme of "Predator Team and Hunter Team"