1) Fading HUD in multiplayer. Why don't we have this already? Seems like an oversight. It would also be nice to be able to turn off the gun silhouette permanently, leaving only the ammo meter/reload bar when reloading. Maybe also an option for changing the color of the HUD items/reticle.
2) Change all grenade alerts to general ones (as opposed to "FRAG!" or "SMOKE!"); remove the alert from the throwing character, allowing the player to communicate this alert through his headset if necessary. I think it's unlikely that an opponent would identify a grenade type (frag v. smoke) in flight, and I think that it's unlikely that an aggressor would alert his target of what he's throwing.
3) Independent sensitivity settings for zoomed mode and "external" mode. This may not be feasible, but it'd be nice to be able to slow down sniper aiming while still being able to turn tight corners while moving.