Programmable unit AI
Giving players more control over the unit level AI (i.e. how the unit responds in various circumstances or the set of instructions that it has) allows them to efficiently control a larger number of units. As real-time strategy has evolved many unit commands have been added. However, there's still room for expansion. An incomplete list:
Sequence of move coordinates/tasks
Patrol area
Patrol route
Don't move under any circumstances (hold position)
Move to engage enemy (x tiles) but return to position (don't move by more than y tiles)
Autoexplore
Hunt x unit types
When under attack by superior force, retreat to coordinates x,y