If Arma 4 happened - which timeline would you prefer?
Honestly... Cold war arma was done, and we have Reforger for which they could easily just develop missions and a campaign if they wanted to.
Arma 3 with it's near future setting is a hit and miss for me. They really overestimated the capabilities of Eastern powers (especially Iran), really underestimated the importance of drones, and really overestimated the procurement changes (with the US for some reason acquiring Merkava tanks, and reintroducing the A10 Thunderbolt as the "A-164 wipeout" for some reason...
They really missed the mark, drone warfare has really become the bane of any fun tactical squad playing.
I would highly recommend a theoretical Armaverse "Syria" (they could rename it to anything else) incursion circa 2013 or such. This is a year when scout drones were still still there, where the tech is still pretty advanced, but drones aren't nearly as ubiqutuos as they are in our current year.
A soft reboot, with the likes of Russian forces intervening on the side of loyalist government while NATO intervening on the side of rebels would make for plenty of asymmetric fighting while keeping the conventional stuff adjusted for what we know in tech and experiences from early Ukraine/Iraq etc.