It has irked me somewhat that in addition to costing Imperium, mythic units are generally outperformed by T3 units. This is because of unit enchantments, which when layered upon T3 units of various classes, bring them to T4 pretty easily in power level, with the added advantage that you can have as many as you want without crippling your imperium income.
If possible, it would be amazing to add it so that mythic units were Skirmishers, Support, Battle Mage etc. as appropriate to their role. This would allow compatibility with any future content/mods that adds new enchants.
I dont know how feasible this would be, but I think it would make Mythic units more fun and competitive to use.