I think a big problem people are having with understanding "aesthetic decoupling" is that they don't have a frame of reference. I'm not sure how close this will be to what we get in CoT, but Freedom Force has a decoupled aesthetic system that I think can help.
As you can see in the video, the choice of Power Type, Damage (effect), Cost, Knockback or Stun, Distance, Velocity, etc. are on their own page. Think about this page as the baked-in powers and effects for the Power Sets the devs create. Two melee powersets might have similar powers, except one does Crushing Damage with a Knockback (Haymaker) and the other does Fire Damage with a Burn effect (Incinerate).
The effects are only one page though, and the aesthetic portion of the power is on the separate page. Here, you can choose the animation your character plays when you fire off this power, as well as the visual effect the happens all the way from start to impact. Here, you could choose to have the fire attack emanate from your character's head, hand, chest, or shoulder. The fire effect itself could be green, blue, red, or even not fire at all! Maybe your "fire" powers are secretly celestial powers, in which case you might find a golden glow effect instead.
Hopefully this video example helps you all understand how aesthetic decoupling might work in City of Titans. I would love for devs to comment on your system might be similar or different.
City of Heroes:
Altruist, lvl 50 Invul/SS Tank
Ellodie, lvl 50 WP/Fire Tank
Omega Centauri, lvl 50 SS/Invul Brute
Project Carnivore, lvl 50 Claws/Regen Scrapper
Guardian, lvl 50 PB
Marc Century, lvl 50 Invul/EM Tank