A lot of talk recently has been about making trained units play differently but little of it has discussed how to make them look different without consuming tons of resources. Here are a few ideas to make units physically discernible without requiring tons of new assets.

1.  This one is easy and obvious. Modify the skins on armour so they change more in relation to faction colours. The colour of your armour needs to vary much more depending on your faction. Right now all armour is kinda the same colour, even leather. Giving unique colours to armies' armour would go a long way to making them look interesting. Think Warhammer, just painting units makes them stand out.  

2. Vary armor art among the races/modeltypes slightly. So maybe Kraxis keeps the leather skirt but the other fallen lose it, I think it makes the fallen look too much like kingdoms and too Hellenic anyway. Tarth and the other more primitive races could also loose the Hellenic skirting. Simply substituting 2 different types of leather skirting would make a lot of units look heavily distinct, without requiring basically any new art. You could also throw different shoulder pads on some races.

3. This one would require some real work. Add helmet decorations tied to race. These would be simple art assets that would be added to the basic helmets in the artdefs. Like feathers, horns, horsetails, wings, spikes, antlers, and Roman crests. So for example all Ironner helmets would gain viking horns.

Factions' units would look very very different from each other if something like these changes are implemented.