Yeah I'd like more Arma2 style. But if I could wave a magic wand and get the dream Arma4, I'd have them figure out how to do 64bit data streaming well, and have much larger maps. 250km is awesome when you are on foot, but in a jet you can't fly for more than a few seconds without thinking about turning around. In Arma2 you could fly outside of Chernarus and it would create some empty looking landscape which at least felt less restrictive. But I'd really like to see some innovation that could allow big maps. Either flight sim size (600km squared?) or the whole hog like Minecraft, have it generate hills and valleys and cities endlessly, but with good graphics. The main thing is big and interesting regions. I miss Takistan, those huge Afghani mountain ranges were awesome for flying gunships and jets. The dream would be to have 1000 mile map or more and have some players fighting in a forest, and have them call in an airstrike that's 10 minutes away.
Besides that I think they need to start doing all their missions with set pieces that spawn as you approach. Some of the missions I played were so much better because of that. As soon as you fill up a mission in the editor, it runs like crap. But if the enemies only spawn just outside your visual range as you approach, then you can have complex missions without killing the frame rate. They should add this functionality in the editor so you can click trigger, spawns enemies, then you set up the enemies. Maybe they are an ambush, maybe they are chilling unaware, the map maker can set this up and have it trigger when the player gets close. And they should make stuff de-spawn too. Currently you can do this but it's not part of the editor.
Most of all I think they should come up with an all encompassing game mode that showcases all of Arma's features. Something like King of the Hill but bigger, less Playstation, more use of vehicles. And again bigger areas, people seem to struggle with balancing aircraft to not just bomb everyone and ruin everyones fun (except the pilot), but all they need to do is spread things out. Again in the Takistan map with CTI, I used to hunt people with gunships and jets and I loved every minute. But half the towns were controlled by the enemy and they could shoot me down with AA guns and missiles and shit so it wasn't overpowered. It balanced itself really well. Most modes are stupid because as soon as the planes go up, it becomes a Michael Bay movie, or they just don't have aircraft. And they need to figure out persistent worlds. All these multiplayer modes suck for me because whenever I want to play, the servers with decent ping are mid mission. And the missions only last an hour or so anyway, so there's no time to get stuck in. And again in Arma2OA CTI you got to control troops and vehicles more like an RTS. If you wanted. They seem to have given up on that now. It's in Arma3 but it's not in most of the missions people play. I would unify the players with a killer mode.