Personally, I'd like to see:
*Better weapon reload animations that are remotely realistic.
*An AC130 SPECTRE gunship to provide fire-support.
*The ability to call in mortar/artillery fire.
*A specific CAS system on radios, and the ability to select a position you want blown up, then transmitting that information.
*Helicopters/Jets crash-landings that the pilot can survive (tail rotor shot off, engine failure, whatever) with/without injuries.
*Weapons jamming from time to time, with the jam probability changing for each weapon on different terrains.
*Ragdoll physics.
*Improved rifle physics with decent sniping weapons, Not just M21s/Dragunovs - M24SWS, M82, L96A2, Mk12 SPR Mod0 etc. And multiple target pentration.
*Being able to dig-in and create a prepared position.
*Far better AI, who act like humans under fire. For example, a civilian wouldnt stand around if you discharged your rifle into the air; they would make a run for it. And just because you may put out 2 more rounds than the AI soldier next to you, you shouldnt become the prime target.
*Ability to drop large amounts of airborne troops from C130s/C5s/C17s for invasions etc.
Thats what id like to see, hopefully ArmA should be the answer to my prayers.