Tasunke's brand of Faction Differentiation
Example:I think the Wraiths should have a custom ability or weapon.
For now lets give them Vampiric Sword. It drains life (health) on strike and perhaps also gives a strength debuff.
->could replace either short sword or broad sword
->Wraiths are physically weaker, so giving their armies the ability to 'drain life' in melee could make them a bit more competitive if they focused on the warfare path.
(not sure if it should be early in the magic tree or mid-way in the warfare tree, something to think about)
Also, a free spell for any Wraith Champion. "Steal Spell/Drain Spirit" its a direct damage spell on an enemy caster, it debuffs them by 40% spell power, and steals a random spell sphere. (or at least has a chance to steal a spell sphere).
Something that should be available to any Fallen (or at least Umber and Resolyn ... possibly quendar.) should be Path of the Necromancer
-> requires Path of the Mage and Death II
-> focuses on summons of 'massive' undead armies
-> focuses on turning killed enemy units into new (permanent) skeleton armies
ie: Grave Curse -> Once the enemy is killed, it returns as a permanent undead ally (I think we already have lurks and the like, which are nice but minor, as it doesn't use the enemy's weapons and traits against them)
Perhaps a unit turning undead might lose a few traits ... but should probably keep all (or most) of their traits and levels.
-> Probably shouldn't work on a Champion though, since they don't technically 'die' but re spawn.\
For Trogs ... maybe their strength and constitution traits could be more cost effective (better OR cheaper), to make up for their lack of life mana.
Or maybe give the Trogs/Yithril their own version of "Aura of Vitality". (unique to trogs)
(Trogs could be given spells that enhance their fighting abilities while the rest get stuff like Necromancy)
Trogs could also get Cloak of the Iron Hide ... which gives +8 ranged defense and ranged dodge, while reducing movement by 1.
Trogs should probably pay half-maintenance on any military buildings.
Meanwhile Gilden and pariden could pay half-maintenance for certain economic/diplomatic buildings.
Capitar could have more access to gold producing buildings. If Capitar take over a Tarth City, maybe the city should remain "Tarth" with higher unrest, yet the ability to make a specialized SLAVE PEN ++ which more than makes up for it 
Meanwhile Altar could suffer only HALF of the champion stack penalty ... and get +2 strategic move when using a stack of only Champions. (in addition to all the extra exp and prestige from completing quests)
-> Perhaps additional options in quests, in order to get more champions or extra quest-related items.