I want to see a immersive modification system , combining the handheld titles with the one in infinity , I.E: In SP you can equip as much parts as you can fit in your aircraft as long as they don't overlap (you can't have 2 kinds of enhanced engines) while in MP you could do the same but limited to the number of slots your aircraft has (like infinity). This should not be only statistical but also cosmetic (if you add a COFFINSYS to your plane , the cockpit will change as well)
Home bases. You can manage your own airbase (in lieu of MGSV) adding more hangars to store your planes , barracks to optimize your crew and research labs to develop your planes. At later levels you also can build an automated hangar to quickly build any aircraft. This does not limit your bases to airfields , you could also get yourself an aircraft carrier or sub carrier , hell , an Aigaion too.
Wide cockpit view that lets you see all of it.
Open worldish , you can freely fly arround your base and any battlefield and meet other players flying over there , as long as your base has the support to deploy your plane over longer distances (you would need refueler plane or aircraft carriers to enable you to get in places distant to your base) but if you have any type of carrier , you can do this easier. To navigate to other battlefields you fly to the edge of the map and a transition will take place with a intersection in order to refuel.
Manage your own airforce , from elites to aspirants and of course your aces , who will fly in your squad. From scout bi-planes to stealth bombers....or arkbird....
STRAGEREAL , i don't care what reasons there is to not revisit Strangereal , but i don't think Ace Combat truly is Ace Combat outside of strangereal.
Anyway , this is my wishes , tell what you think about 'em or what you wish to see. Cheers