With the removal of stacks and introduction of unit ranges, line of sight becomes more important. It might be interesting in late game to be able to manipulate lines of sight. This is the premise behind electronic warfare. It also introduces some elements from stratego.

Here are my preliminary ideas for Electronic warfare options based on my limited knowledge of Civ4. They are only meant to demonstrate the idea of E-War. I have no idea how air combat will be implemented, thus did not propose any idea for airborne ECM.

Electronic Warfare Promotions
ECM 1 – The Unit become invisible on enemy Radar
ECM 2 – The Unit is permanently shrouded in fog of war unless it attacks or is attacked.
ECCM – Require ECM2, The Unit peel back fog of war generated by electronic warfare or abilities.
Decoys – Require ECM2, This unit occupies adjacent Hexes with ghost copies of random units, unless these cells are already occupied. Decoys also show up on enemy radar. Unit attacking decoys loses a turn, missiles attacking decoys are lost.
Masking – Requires ECM2, This unit appear as another unit unless it’s in combat with another unit.

Electronic Warfare Units
Mobile Radar – Require Radio – A ground unit that locate units in fog of war, but do not reveal their type.
Mobile ECM – Require Radio, Stealth – Information age upgrade for the mobile radar. Hide nearby units from enemy radar. Start with ECM 2.
Forward Command – Require Radio, Computers – Information age upgrade for the mobile radar. Increase the interception chance of nearby units with intercept. Start with ECCM.

Electronic Warfare Buildings
Radar Station – Require Radio - Locate units in fog of war over tremendous distances – but do not reveal their type.
Signal Intelligence – Require Radio, Computers - Information age building. Further increase the city’s radar range, produce spy point.