I was just rewatching the awsome release trailer rendered in the game engine.
If you notice at the following moment you can see the elf creeping at a Chaos warrior which is clearly stylised to look like a leader/officer type (3 minutes 00 seconds in):
This made me thinking. Could you add a new class of enemies for both factions. A leader type, which buffs the enemies, maybe can bring more reinforcements/waves until you kill him? The Shade class is clearly designed to go after high value targets and some classes have the similar idea behind them with specific weapon choices. This would introduce a bit more complexity to enemy encounters.